Sheet conveying apparatus and image forming apparatus

Abstract

A sheet conveying apparatus includes a first conveying member configured to rotate in contact with a sheet, a second conveying member disposed at a position different from that of the first conveying member in a sheet conveying direction, a motor, a first rotating member connected to the motor, a second rotating member connected to the first conveying member, and an elastic member engaged with the first and second rotating members, the elastic member being deformable to allow the first conveying member to rotate in a state where an angular velocity of the first rotating member driven by the motor is different from an angular velocity of the second rotating member.

Description

Technical Field

[0001] This disclosure relates to a sheet conveying apparatus for conveying sheets and an image forming apparatus for forming images on the sheets. Background Technology

[0002] Japanese Patent Application Publication No. H07-234604 discloses an image forming apparatus that includes independent drive systems for driving a fixing unit and a transfer unit respectively, detecting the looped amount of a sheet formed on the sheet before entering the inlet of the fixing unit, and controlling the drive speed of the fixing unit based on the detected looped amount. Summary of the Invention

[0003] This disclosure provides a sheet conveying apparatus and an image forming apparatus that can convey sheets more stably.

[0004] One aspect of this disclosure provides a sheet conveying apparatus comprising: a first conveying member configured to rotate while in contact with a sheet to convey the sheet in a sheet conveying direction; a second conveying member disposed at a position different from that of the first conveying member in the sheet conveying direction, the second conveying member being configured to rotate while in contact with the sheet to convey the sheet during at least a portion of a time period during which the first conveying member is in contact with the sheet; a motor configured to drive the first conveying member and the second conveying member; a first rotating member connected to the motor and configured to rotate; a second rotating member connected to the first conveying member and configured to rotate; and an elastic member engaging with the first rotating member and the second rotating member, the elastic member being deformable to allow the first conveying member to rotate when the angular velocity of the first rotating member driven by the motor is different from the angular velocity of the second rotating member.

[0005] The features of this disclosure will become clear from the following description of embodiments with reference to the accompanying drawings. The following description of the embodiments is given by way of example. Attached Figure Description

[0006] Figure 1 This is a schematic diagram of an image forming apparatus according to the first embodiment.

[0007] Figures 2A to 2E Each is a view showing the transfer state of the sheet between the transfer clamp and the fixing clamp.

[0008] Figure 3A The drive delivery path in the first embodiment is shown. Figure 3B and Figure 3C The modified driver delivery path is shown in the example.

[0009] Figure 4A This is an exploded view of the drive transmission unit in the first embodiment. Figure 4B This is a perspective view of the drive transmission unit in the first embodiment. Figure 4C This is a cross-sectional view of the drive transmission unit in the first embodiment.

[0010] Figures 5A to 5C Each is an illustrative view relating to the angular velocity of the element involved in the drive transmission according to the first embodiment.

[0011] Figures 6A to 6D Each view is a modified example using multiple torsion springs.

[0012] Figure 7A and Figure 7B Each is an illustrative view of a modified example using multiple torsion springs.

[0013] Figure 8A and Figure 8B Each is a view showing an example of a modification using both a torsion spring and a torque limiter.

[0014] Figures 9A to 9C Each is an illustrative view of the operation of the torque limiter based on the modified example.

[0015] Figure 10 This is an exploded view of the drive transmission unit according to the second embodiment.

[0016] Figures 11A to 11C Each is a view showing the transfer state of the sheet between the alignment clamp and the transfer clamp.

[0017] Figure 12 This is a view showing the drive delivery path according to the second embodiment.

[0018] Figures 13A to 13C Each is an illustrative view relating to the angular velocity of the element involved in the drive transmission according to the second embodiment.

[0019] Figures 14A to 14C Each is an illustrative view of the angular velocity of the element involved in the drive transmission, based on the modified example.

[0020] Figure 15 This is a schematic diagram of an image forming apparatus according to a third embodiment. Detailed Implementation

[0021] Embodiments relating to this disclosure will now be described with reference to the accompanying drawings.

[0022] First Embodiment

[0023] Figure 1 This is a cross-sectional view of an image forming apparatus 100 according to a first embodiment used as one example. The image forming apparatus 100 is a four-color full-color laser printer, that is, an electrophotographic image forming apparatus employing electrophotographic processing, and includes four processing cartridges PY, PM, PC, and PK serving as first to fourth cartridges. For example, the image forming apparatus 100 forms an image on a sheet S based on image information received from an external device.

[0024] The number of processing cartridges in an electrophotographic image forming apparatus is not limited to four, and the apparatus may be a monochrome laser printer comprising only one processing cartridge. Furthermore, the term "image forming apparatus" is not limited to a single-function printer having the function of forming an image on a sheet S based on image information received from an external device, but may also refer to a copier, fax machine, or a multifunction device combining these functions.

[0025] In the following description and accompanying drawings, with respect to the image forming apparatus 100, the front side refers to the side where the door 31 is provided, and the rear side refers to the side opposite to the door 31. The front-rear direction is the direction from the rear side of the image forming apparatus 100 towards the front side, i.e., the forward direction, and the opposite direction, i.e., the rear direction. With respect to the image forming apparatus 100, the left-right direction is the left-right direction when the image forming apparatus 100 is viewed from the front side. With respect to the image forming apparatus 100, the up-down direction is the vertical direction when the image forming apparatus 100 is mounted on a horizontal plane, i.e., the direction of gravity.

[0026] According to the terminology of this disclosure, "sheet conveying device" refers to, for example, a conveying device for conveying a sheet S used as recording material (i.e., a recording medium) in an image forming apparatus. The "sheet conveying device" may be part of the image forming apparatus body equipped with image forming functions, or it may be disposed on a device independent of the image forming apparatus body. The portion of the image forming apparatus 100 according to this embodiment, excluding the processing boxes PY to PK used as the image forming section, is an example of a sheet conveying device.

[0027] Overall configuration of image forming equipment

[0028] like Figure 1 As shown, the image forming apparatus 100 includes an apparatus body 100A and processing cartridges PY, PM, PC, and PK. The processing cartridges PY to PK are detachably attached to the apparatus body 100A. The apparatus body 100A refers to the portion of the image forming apparatus 100 excluding the processing cartridges PY, PM, PC, and PK.

[0029] The box storage section, which serves as installation space for storing the processing boxes PY, PM, PC, and PK, is located inside the main body 100A. The four processing boxes PY, PM, PC, and PK are stored in predetermined attachment positions within the box storage section, with their orientation approximately horizontal from the rear to the front of the main body 100A.

[0030] Each of the processing cartridges PY to PK is an example of an image forming section for forming an image to be recorded on a sheet conveyed within the image forming apparatus 100. Each of the processing cartridges PY to PK includes a photosensitive drum 1 serving as an image carrying member and at least one processing member acting on the photosensitive drum 1 to perform electrophotographic processing. Each processing cartridge PY to PK according to this embodiment includes a charger 2 serving as a charging unit, a developing unit 3 serving as an image developing unit, and a cleaning unit 4 serving as a cleaning unit.

[0031] The first processing cartridge PY stores yellow toner in the developing unit 3 and forms a yellow toner image on the surface of the photosensitive drum 1. The second processing cartridge PM stores magenta toner in the developing unit 3 and forms a magenta toner image on the surface of the photosensitive drum 1. The third processing cartridge PC stores cyan toner in the developing unit 3 and forms a cyan toner image on the surface of the photosensitive drum 1. The fourth processing cartridge PK stores black toner in the developing unit 3 and forms a black toner image on the surface of the photosensitive drum 1.

[0032] In addition, the main body of the equipment 100A includes a scanner unit 11, a transfer unit 12, a fixing unit 23, a feed unit 18, an alignment roller pair 20a, and a sheet discharge roller pair 24.

[0033] Scanner unit 11 is arranged above processing cartridges PY to PK. Scanner unit 11 is an example of an exposure unit for exposing the photosensitive drum 1 of each of processing cartridges PY to PK. Scanner unit 11 outputs a laser modulated based on image information and scans and exposes the surface of the photosensitive drum 1 of the respective processing cartridges PY to PK through an exposure window 6 provided on the upper side of the cartridge frame 5. An LED exposure unit using an LED as a light source can be used as the exposure unit.

[0034] The transfer unit 12 is configured to form a transfer clamping part Nt, and to transfer the toner image onto the sheet S while clamping and conveying the sheet S through the transfer clamping part Nt. In this embodiment, the transfer unit is driven by a motor M, which serves as a drive source shared with the fixing unit 23.

[0035] The transfer unit 12 is arranged below the processing boxes PY to PK. The transfer unit 12 includes an intermediate transfer belt 13 serving as an intermediate transfer body, a belt drive roller 14, a steering roller 15, a tension roller 16, a belt cleaning unit 12a, and a secondary transfer roller 22.

[0036] The intermediate transfer belt 13 is formed of a dielectric material and has a flexible annular film component (i.e., a sheet component). The intermediate transfer belt 13 is stretched across the belt drive roller 14, the guide roller 15, and the tension roller 16, and is driven to rotate by the rotation of the belt drive roller 14. The belt drive roller 14 and the guide roller 15 are arranged on the rear side within the equipment body 100A. The tension roller 16 is arranged on the front side within the equipment body 100A. The belt cleaning unit 12a includes a cleaning component that cleans the surface of the intermediate transfer belt 13 as it rotates.

[0037] Regarding the intermediate transfer belt 13, the portion stretched by the cross-belt drive roller 14 and tension roller 16 is referred to as the upper portion, and the portion stretched by the cross-tension roller 16 and guide roller 15 is referred to as the lower portion. With the processing cartridges PY to PK each attached to their respective attachment positions, the lower surface of each photosensitive drum 1 contacts the upper surface of the upper portion of the intermediate transfer belt 13. Four primary transfer rollers are arranged inside the intermediate transfer belt 13 facing each photosensitive drum 1, and the intermediate transfer belt 13 is inserted between the primary transfer rollers and the photosensitive drums. The clamping portion between each photosensitive drum 1 and the intermediate transfer belt 13 is a primary transfer portion, where a primary transfer of the image is performed.

[0038] The secondary transfer roller 22 contacts the belt drive roller 14 of the transfer unit 12, and the intermediate transfer belt 13 is inserted between the secondary transfer roller and the belt drive roller. The transfer clamping part Nt (that is, the secondary transfer clamping part) serves as the clamping part between the secondary transfer roller 22 and the intermediate transfer belt 13, and is the secondary transfer part that performs the transfer of the toner image onto the sheet S. The secondary transfer roller 22 is a conveying member that clamps and conveys the sheet S together with the intermediate transfer belt 13 at the transfer clamping part Nt. The secondary transfer roller 22 is an example of a relative member (that is, a second relative member) facing the intermediate transfer belt 13. The intermediate transfer belt 13 and the secondary transfer roller 22 are examples of a pair of conveying members or roller pairs (that is, a second pair of conveying members or a second pair of rollers) that clamp the sheet S.

[0039] The image forming mechanism 100B, which includes the aforementioned processing boxes PY to PK, scanner unit 11, and transfer unit 12, is used as an image forming part to form an image (i.e., a toner image) on the sheet S.

[0040] The feed unit 18 is arranged below the transfer unit 12. The feed unit 18 includes a feed tray 19 (i.e., a storage section) in which sheets S are stacked and stored, a feed roller 20 serving as a feed component, and a pair of separation rollers 21.

[0041] Various types of sheet components with different sizes and materials, such as paper including plain paper and thick paper, plastic film, cloth, coated paper and other sheet components with surface treatments, as well as sheet components with special shapes such as envelopes and index paper, can be used as sheet S, which is used as recording material (i.e., recording medium). The feed tray 19 adopts a so-called front-loading configuration, wherein the tray can be pulled forward from the device body 100A and inserted rearward into a predetermined attachment position within the device body 100A.

[0042] The fixing unit 23 is configured to form a fixing clamping portion Nf, and fixes the toner image onto the sheet S while clamping and conveying it through the fixing clamping portion Nf. The fixing unit 23 is arranged in the upper part of the rear side within the main body 100A. The fixing unit 23 is a unit that applies heat and pressure to the sheet S on which the toner image has been transferred to perform image fixing processing (i.e., an image heating device). The fixing unit 23 includes a fixing film assembly 23a and a pressure roller 23b serving as a pressing member. The fixing film assembly 23a is an example of a opposing member (i.e., a first opposing member) opposite or facing the pressure roller 23b. The pressure roller 23b and the fixing film assembly 23a are examples of a pair of conveying members or roller pairs (i.e., a first conveying member pair or a first roller pair) that clamp the sheet S.

[0043] The fixing film assembly 23a includes a film serving as a fixing member (i.e., a heating member), a heater 23c serving as a heating unit, and a heater support holding the heater 23c. The film is a flexible tubular member. The heater 23c and the heater support are disposed within the internal space of the film. The heater 23c and the heater support are arranged to be in pressure contact with the pressure roller 23b, and the film is inserted between the heater and the heater support and the pressure roller. Thus, a fixing clamping portion Nf is formed between the pressure roller 23b and the film. The heater 23c and the heater support can be referred to as a clamping portion forming unit.

[0044] Rigid cylindrical rollers or annular belts stretched across multiple rollers can be used as fixing components. Halogen lamps that emit radiant heat when energized or coils that generate heat within the fixing component itself through induction heating can also be used as heating units.

[0045] The sheet discharge roller pair 24 is positioned above the fixing unit 23. The sheet discharge roller pair 24 is the sheet discharge unit for discharging the sheet S. A sheet discharge tray 25 is formed on the upper surface of the equipment body 100A, and the sheet S discharged by the sheet discharge roller pair 24 is supported on the sheet discharge tray. The sheet discharge roller pair 24 includes a sheet discharge roller 24a and a sheet discharge follower roller 24b.

[0046] In this embodiment, the term "roller" used as a component constituting a roller pair generally refers to a drive roller that rotates by being supplied with driving force from a drive source via a drive transmission component such as a gear train. Furthermore, according to this embodiment, the term "follower roller" used as a component constituting a roller pair generally refers to a driven roller that rotates (i.e., rotates together) in tandem with the drive roller. Where the drive transmission component can be suitably configured, the positions of the roller (i.e., the drive roller) and the follower roller (i.e., the driven roller) can be interchanged. Furthermore, both rollers constituting a roller pair can be drive rollers. "Driver-driven roller pair" means that the drive source drives the drive rollers.

[0047] Furthermore, motors M and M1, which serve as drive sources, are installed in the main body 100A of the equipment. Motor M drives the intermediate transfer belt 13 and pressure roller 23b to rotate. Motor M1 drives the feed roller 20 and the separation roller pair 21 to rotate.

[0048] According to this embodiment, the pressure roller 23b is an example of a first conveying member that contacts and rotates with the sheet S and conveys the sheet S along the sheet conveying direction. The intermediate transfer belt 13 is an example of a second conveying member arranged at a different position from the pressure roller 23b (i.e., the first conveying member) in the sheet conveying direction. This second conveying member contacts and conveys the sheet S at least for a portion of the time period during which the pressure roller 23b contacts and rotates with the sheet S. In other words, the intermediate transfer belt 13 and the pressure roller 23b are configured such that there exists a time period during which both simultaneously contact a single sheet S. Furthermore, "sheet conveying direction" refers to the direction of movement of the sheet S conveyed along the conveying path passing through the transfer clamping part Nt and the fixing clamping part Nf.

[0049] The outer peripheral surface 23b1 of the pressure roller 23b is an example of the first contact surface that contacts the sheet S. The outer peripheral surface 13a of the intermediate transfer belt 13 is an example of the second contact surface that contacts the sheet S.

[0050] Furthermore, in this embodiment, the pressure roller 23b is arranged adjacent to the transfer clamping portion Nt in the sheet conveying direction. That is, the pressure roller 23b is arranged at the fixing clamping portion Nf, where the sheet S conveyed in the sheet conveying direction receives a force (i.e., a conveying force) in the sheet conveying direction after the transfer clamping portion Nt.

[0051] Image forming operations

[0052] An image forming operation will be described, which is a series of operations performed by the image forming apparatus 100 to form an image on the sheet S while it is being transported. The image forming apparatus 100 begins the image forming operation upon receiving an instruction to perform image forming along with image information. The following describes the case of forming a panchromatic image on the sheet S.

[0053] First, the photosensitive drum 1 of each processing cartridge PY, PM, PC, and PK is driven to rotate counterclockwise at a predetermined circumferential speed in the figure. The intermediate transfer belt 13 is also driven to rotate in the same direction as the rotation of the photosensitive drum 1 (that is, clockwise in the figure) at a speed corresponding to the circumferential speed of the photosensitive drum 1. The circumferential speed of the intermediate transfer belt 13 determines the transfer speed at which the toner image is transferred onto the sheet S at the transfer clamping part Nt, that is, the image forming speed in the sub-scanning direction, which is also referred to as the processing speed. In addition, the scanner unit 11 is driven in parallel with the driving of the photosensitive drum 1 and the intermediate transfer belt 13. The scanner unit 11 is driven by an image signal (also called a video signal), which is a time-series signal converted from image data formed by decomposing image information input from an external computer to the image forming apparatus 100 into component images of individual toner colors.

[0054] In each of the processing cartridges PY to PK, a charger 2, with an applied charging voltage, uniformly charges the surface of the photosensitive drum 1 to a predetermined polarity and potential. The scanner unit 11 exposes the surface of each photosensitive drum 1 based on an image signal, thereby forming an electrostatic latent image on the surface of each photosensitive drum 1 corresponding to a component image of each color. The electrostatic latent image is developed into a toner image, i.e., a developer image, by using toner supplied from the developing unit 3 as a developer.

[0055] Through the above operations, yellow, magenta, cyan, and black toner images are formed on the four photosensitive drums 1 of the processing cartridges PY, PM, PC, and PK. The toner images are transferred to the intermediate transfer belt 13 in a single transfer section. During this process, by performing a single transfer, toner images of other colors are superimposed on the toner images already transferred, forming a full-color toner image on the intermediate transfer belt 13. In each processing cartridge from PY to PK, the cleaning unit 4 removes toner residue remaining on the photosensitive drum 1 that has not been transferred to the intermediate transfer belt 13, i.e., residual toner.

[0056] In parallel with the operation of the image forming mechanism 100B described above, the sheet conveying operation of the sheet S is performed as follows. First, the motor M1, which serves as the drive source, is started, and the feed roller 20 and the separation roller pair 21 are driven to rotate by the driving force of the motor M1. The feed roller 20 contacts the uppermost sheet S of the sheet bundle supported on the feed tray 19, rotates, and feeds the sheet. The separation roller pair 21 includes a transfer roller for further conveying the sheet S received from the feed roller 20 and a separation roller that is in pressure contact with the transfer roller. The separation roller is attached to a roller shaft fixed to the equipment body 100A via a torque limiter. The separation roller allows only one sheet S in contact with the transfer roller to pass through the separation clamping part by applying a frictional force to the sheet S passing through the separation clamping part between the transfer roller and the separation roller, and prevents other sheets S from passing through the separation clamping part. The separation roller pair 21 is an example of a conveying member for separating and conveying the sheet S, and for example, a pad-shaped rubber member (i.e., a separation pad) can be used instead of the separation roller.

[0057] The sheet S fed from the separating roller pair 21 is conveyed to the alignment roller pair 20a. The alignment roller pair 20a includes an alignment roller 20b and an alignment driven roller 20c. The alignment driven roller 20c is an example of an opposing member facing the alignment roller 20b. The alignment roller 20b and the alignment driven roller 20c are examples of a pair of conveying members or rollers that clamp the sheet S. Furthermore, a baffle that can move between a closed position and an open position is provided near the alignment roller pair 20a. In the closed position, the alignment clamping portion Nr, which is the clamping part of the alignment roller pair 20a, is closed, and in the open position, the clamping portion is released.

[0058] The conveying of the leading edge of sheet S is restricted by abutting against a baffle in the closed position. The baffle is pushed to the closed position by a pressing member so that no pivoting occurs at the point when the leading edge of sheet S contacts it. After the leading edge of sheet S abuts against this abutting portion, as sheet S continues to be conveyed by the upstream side roller pair (separation roller pair 21 in this embodiment), sheet S bends between separation roller pair 21 and alignment roller pair 20a. In this state, the leading edge of sheet S turns to align with the baffle, and the skew of sheet S is corrected.

[0059] Subsequently, as the bending of the sheet S increases between the upstream side roller pair and the alignment roller pair 20a, the force acting on the baffle in the conveying direction increases due to the elastic force of the sheet S (i.e., the force in the expansion direction to eliminate bending). When this force exceeds the pushing force of the pressing member, the baffle retracts to the open position, and the leading edge of the sheet S enters the alignment clamping part Nr. The configuration of using a baffle to perform skew correction of the sheet S has been described above, but for example, skew correction of the sheet S can also be performed by having the leading edge of the sheet S abut against the alignment clamping part Nr while the alignment roller pair 20a is in a stopped state.

[0060] Subsequently, at a time matching the arrival time of the toner image formed on the intermediate transfer belt 13 at the transfer clamping section Nt, the alignment roller pair 20a begins to drive, and the alignment roller pair 20a conveys the sheet S to the transfer clamping section Nt. By supplying a secondary transfer bias to the secondary transfer roller 22 at the transfer clamping section Nt, the toner image on the intermediate transfer belt 13 is electrostatically transferred to the sheet S. At the transfer clamping section Nt, the sheet S is clamped by the intermediate transfer belt 13 and the secondary transfer roller 22, and is conveyed toward the fixing unit 23 by the circumferential speed (i.e., the processing speed) of the intermediate transfer belt 13. The belt cleaning unit 12a removes the toner remaining on the intermediate transfer belt 13 that has not been transferred to the sheet S, i.e., the residual toner.

[0061] While the fixing unit 23 clamps and transports the sheet S through the fixing clamping part Nf, it applies heat and pressure to the toner image on the sheet S. This performs the mixing of the various toner colors and their fixing on the sheet S. The sheet S, having passed through the fixing unit 23, is discharged from the outside of the equipment body 100A by the sheet discharge roller pair 24 and supported on the sheet discharge tray 25.

[0062] The secondary transfer roller 22 is pushed toward the intermediate transfer belt 13 by a pressing member (i.e., a spring member, not shown) with a predetermined pressing force (e.g., 4 kgf). This generates pressure between the secondary transfer roller 22 and the intermediate transfer belt 13 at the transfer clamping portion Nt, which is the clamping pressure. The magnitude of the pressing force, which limits the clamping pressure of the transfer clamping portion Nt, is set by taking into account the width of the transfer clamping portion Nt in the sheet conveying direction, the difference in width between the center and the end of the transfer clamping portion Nt of the secondary transfer roller 22 in the direction of rotation axis, and the adhesion between the sheet S and the intermediate transfer belt 13.

[0063] In this state, when the sheet S does not slide relative to the conveying member, the maximum value of the frictional force received by the sheet S at the clamping portion of the conveying member is called the holding force Ft of the sheet S at the clamping portion. Figure 2B With the pressing force of the secondary transfer roller 22 set to the aforementioned value (4 kgf), the holding force Ft of the sheet S at the transfer clamping part Nt is, for example, 1 kgf. This means that if the sheet S held by the transfer clamping part Nt is pulled upstream or downstream in the sheet conveying direction with a force equal to or greater than 1 kgf, the sheet S will slide relative to the intermediate transfer belt 13.

[0064] When the sheet S slides relative to the intermediate transfer belt 13 during the transfer of the toner image, the transferred image may be disturbed. The sliding property of the sheet S also varies depending on the amount of toner transferred at the transfer clamping part Nt. In order to suppress the sliding of the sheet S, it is preferable to increase the holding force Ft of the sheet S at the transfer clamping part Nt by increasing the clamping pressure of the transfer clamping part Nt.

[0065] Furthermore, the fixing film assembly 23a of the fixing unit 23 is pushed toward the pressure roller 23b by a pressing member (i.e., a spring member, not shown) with a pressing force of 20 kgf. This generates pressure (i.e., clamping pressure) between the fixing film assembly 23a and the pressure roller 23b at the fixing clamping part Nf. The clamping pressure of the fixing clamping part Nf is set taking into account the fixing properties or gloss of the image.

[0066] If the pressing force of the fixing film assembly 23a is set to the above value (20 kgf), then the holding force Ff of the sheet S at the fixing clamping part Nf ( Figure 2B For example, equal to or greater than 5 kgf. That is, the holding force Ff of the sheet S at the fixing clamping part Nf is greater than the holding force Ft of the sheet S at the transfer clamping part Nt.

[0067] Pressure roller drive configuration

[0068] According to this embodiment, the pressure roller 23b has a diameter of 20 mm and is driven by a motor M, which serves as the drive source. The necessary torque for rotating the pressure roller 23b (that is, the load torque of the pressure roller 23b) can fluctuate in the range of 2 kgf cm to 3.5 kgf cm due to the dispersion of the pressing pressure of the fixing clamping part Nf. Furthermore, the pressure roller 23b thermally expands due to the heat generated by the heater 23c.

[0069] Due to factors such as outer diameter tolerances during the manufacturing of pressure roller 23b, the values ​​of the circumferential speed VB of the intermediate transfer belt 13 and the circumferential speed VF of the pressure roller 23b during image formation may differ. That is, even when the angular velocities of the pressure roller 23b and the belt drive roller 14 are constant relative to the output shaft of the motor M, the circumferential speeds VB and VF of the pressure roller 23b and the intermediate transfer belt 13 can be different values. For example, as... Figure 2B As shown, with the circumferential speed VB of the intermediate transfer belt 13 at 100%, the pressure roller 23b can rotate at approximately 103% of the circumferential speed VF. Due to this speed difference, in the time it takes for the outer circumferential surface of the intermediate transfer belt 13 to move a distance corresponding to the long side (297 mm) of the A4 size sheet S, the outer circumferential surface of the pressure roller 23b moves a distance approximately 9 mm longer (306 mm) than the intermediate transfer belt 13.

[0070] Now, since the holding force Ff of the sheet S at the fixing clamping part Nf is greater than the holding force Ft of the sheet S at the transfer clamping part Nt, if the relationship VF>VB is realized, the sheet S may slide relative to the intermediate transfer belt 13. That is, the sheet is conveyed at a circumferential speed VF of the pressure roller 23b, and the sheet S may slide relative to the intermediate transfer belt 13 rotating at a circumferential speed VB, thereby interfering with the transferred image.

[0071] like Figure 3A As shown, according to this embodiment, the driving force is transmitted from the motor M, which serves as the driving source, to the pressure roller 23b via the drive transmission unit DT, which includes a torsion spring 40 (i.e., a torsion coil spring). The intermediate transfer belt 13 according to this embodiment rotates by the driving force transmitted by the motor M, which serves as the common driving source, causing the belt drive roller 14 to rotate.

[0072] Drive transmission unit

[0073] Reference Figure 3A and Figures 4A to 4C The description includes the drive transmission unit DT of the torsion spring 40. Figure 4A This is an exploded diagram of the drive transmission unit DT. Figure 4B This is a perspective view of the drive transmission unit DT. Figure 4C This is a cross-sectional view of the drive transmission unit DT.

[0074] The drive transmission unit DT includes an input gear 51 serving as a first rotating member (i.e., an input-side rotating member), an output gear 52 serving as a second rotating member (i.e., an output-side rotating member), and a torsion spring 40 serving as an elastic member.

[0075] The input gear 51 is connected to the motor M, which serves as the drive source, and rotates under the driving force of the motor M. That is, the input gear 51 is configured such that at least a portion of the driving force output from the motor M enters the input gear 51. The input gear 51 and the motor M can be connected via a drive transmission mechanism such as a gear train or belt drive mechanism, or they can be directly engaged.

[0076] The output gear 52 is connected to the pressure roller 23b, which serves as the first conveying member. The pressure roller 23b is configured to rotate by the driving force of the motor M transmitted via the output gear 52. The output gear 52 and the pressure roller 23b can be connected via a drive transmission mechanism such as a gear train or belt drive mechanism, or they can be directly engaged.

[0077] The torsion spring 40 is a spring member that elastically deforms according to the force (i.e., torque) in the direction of rotation about its central axis. One end of the torsion spring 40 engages with the input gear 51, and the other end engages with the output gear 52. The central axis of the torsion spring 40 can be shared with the rotation axis Ax of both the input gear 51 and the output gear 52. The torsion spring 40 transmits the torque received from the input gear 51 to the output gear 52. That is, the driving force of the motor M is transmitted from the input gear 51 to the output gear 52 via the torsion spring 40.

[0078] According to this embodiment, the input gear 51, the torsion spring 40, and the output gear 52 rotate around a common rotation axis Ax.

[0079] like Figure 4A As shown, arm portions 40a and 40b are formed at both ends of the torsion spring 40. Furthermore, the torsion spring 40 includes a coil portion in which metal spring wire is helically wound between the arm portions 40a and 40b. The torsion spring 40 is arranged such that the coil portion extends in the direction of the rotation axis Ax while rotating around it. That is, the coil portion is wound around the rotation axis Ax. More specifically, the number of turns of the coil portion around the rotation axis Ax is two or more. The torsion spring 40 can be a wire member (i.e., a shaped wire spring), wherein the arm portions 40a and 40b are formed from the same spring wire as the coil portion. That is, the torsion spring 40 is configured to deflect around the rotation axis Ax.

[0080] A spring hook portion (i.e., a first engagement portion) 51a, which engages with one arm portion 40a of the torsion spring 40, is provided on the input gear 51. A spring hook portion (i.e., a second engagement portion) 52a, which engages with the other arm portion 40b of the torsion spring 40, is provided on the output gear 52. According to this embodiment, the spring hook portion 52a is a groove portion extending along a virtual line orthogonal to the rotation axis Ax (i.e., the direction of the rotation radius of the input gear 51 and the output gear 52).

[0081] like Figure 4B and Figure 4C As shown, with respect to the direction of the rotation axis Ax, the arm portion 40a and the spring hook portion 51a are arranged away from the arm portion 40b and the spring hook portion 52a. Furthermore, the input gear 51 and the output gear 52 are positioned away from each other with respect to the direction of the rotation axis Ax.

[0082] The engagement of arm portion 40a and spring hook portion 51a of input gear 51 prevents one end of torsion spring 40 from rotating relative to input gear 51. The engagement of arm portion 40b and spring hook portion 52a of output gear 52 prevents the other end of torsion spring 40 from rotating relative to output gear 52. Furthermore, changes in the angle of torsion spring 40 allow relative rotation between input gear 51 (i.e., the first rotating member) and output gear 52 (i.e., the second rotating member). In other words, the sheet conveying device is configured such that changes in the angle of torsion spring 40 allow relative rotation between input gear 51 (i.e., the first rotating member) and output gear 52 (i.e., the second rotating member).

[0083] The method of engaging or fixing one end and the other end of the torsion spring 40 with the input gear 51 and the output gear 52 is not limited to the methods described above, and for example, the two end portions of the coil portion can be fitted to the recessed portions formed on the two gears by an interference fit. Furthermore, an adhesive can be used to fix one end and the other end of the coil portion of the torsion spring 40 to the input gear 51 and the output gear 52. That is, while the input gear 51 is rotated by the driving force of the motor M, the engagement between the torsion spring 40 and the input gear 51, as well as the engagement between the torsion spring 40 and the output gear 52, is maintained.

[0084] like Figures 4A to 4C As shown, the input gear 51 includes a spring hook portion 51a, a cylindrical portion 51b, a gear portion 51c, and an outer peripheral portion 51f. The input gear 51 may be an integrally molded product in which the spring hook portion 51a, the cylindrical portion 51b, the gear portion 51c, and the outer peripheral portion 51f are formed from the same resin material.

[0085] The cylindrical portion 51b of the input gear 51 is formed in a generally cylindrical or approximately cylindrical shape, with the rotation axis Ax set at the center. The outer peripheral portion 51f is formed in a generally cylindrical shape, with the rotation axis Ax set at the center, so as to surround the outer periphery of the cylindrical portion 51b. The spring hook portion 51a is a groove-shaped portion formed on the outer peripheral portion 51f, which is a groove extending along a direction intersecting with a virtual circle set at the center of the rotation axis Ax. The gear portion 51c is designed to receive driving force from the motor M. Specifically, the gear portion 51c is designed to mesh with a corresponding gear that rotates by the driving force transmitted from the motor M.

[0086] The output gear 52 includes a spring hook portion 52a, a cylindrical portion 52b, a gear portion 52c, and an outer peripheral portion 52f. The output gear 52 may be an integrally molded product in which the spring hook portion 52a, the cylindrical portion 52b, the gear portion 52c, and the outer peripheral portion 52f are formed from the same resin material.

[0087] The cylindrical portion 52b of the output gear 52 is formed in a generally cylindrical or approximately cylindrical shape, with the rotation axis Ax set at the center. The outer peripheral portion 52f is formed in a generally cylindrical shape, with the rotation axis Ax set at the center, so as to surround the outer periphery of the cylindrical portion 52b. The spring hook portion 52a is a groove-shaped portion formed on the outer peripheral portion 52f, which is a groove extending along a direction intersecting with a virtual circle set at the center of the rotation axis Ax. The gear portion 52c is designed to output driving force to the pressure roller 23b. Specifically, the gear portion 52c is designed to mesh with a corresponding gear that rotates together with the pressure roller 23b.

[0088] The torsion spring 40 is attached with one end of its coil portion housed in a slot between the cylindrical portion 51b and the outer peripheral portion 51f of the input gear 51, and the other end of its coil portion housed in a slot between the cylindrical portion 52b and the outer peripheral portion 52f of the output gear 52. The position of the torsion spring 40 is approximately determined relative to the radius of a virtual circle about the axis of rotation Ax by fitting the coil portion into the slot between the cylindrical portions 51b and 52b and the outer peripheral portions 51f and 52f.

[0089] Since the inner diameter of the coil portion fluctuates due to elastic deformation (i.e., deflection) when a load is applied to the torsion spring 40, it is preferable that the outer diameters of the cylindrical portions 51b and 52b are smaller than the inner diameter of the coil portion in the unloaded state. Furthermore, the inner diameters of the outer peripheral portions 51f and 52f are preferably larger than the outer diameter of the coil portion in the unloaded state.

[0090] Furthermore, by fitting the arm portion 40a at one end of the torsion spring 40 to the spring hook portion 51a of the input gear 51, the relative rotation of one end of the torsion spring 40 relative to the input gear 51 is restricted. Similarly, by fitting the arm portion 40b at the other end of the torsion spring 40 to the spring hook portion 52a of the output gear 52, the relative rotation of the other end of the torsion spring 40 relative to the output gear 52 is restricted.

[0091] When motor M starts, the torque driving the motor M enters gear section 51c, and input gear 51 begins to rotate. Simultaneously, output gear 52 attempts to stop rotating, primarily due to the inertia of pressure roller 23b. Therefore, a load in the rotational direction about the rotation axis Ax is applied to torsion spring 40. Due to this load, a torque is generated between arm section 40a at one end and arm section 40b at the other end, causing torsion spring 40 to twist. In other words, the load torque of pressure roller 23b received by torsion spring 40 from output gear 52 and the driving force of motor M received by torsion spring 40 from input gear 51 are in opposite rotational directions about the rotation axis Ax. Therefore, deflection of torsion spring 40 occurs when motor M starts.

[0092] As the angle of the torsion spring 40 deflects, the torque received by the output gear 52 increases by pressing the spring hook portion 52a with the arm portion 40b of the torsion spring 40. When this torque exceeds the load torque of the pressure roller 23b, the output gear 52 and the pressure roller 23b begin to rotate. As described above, the torque value required to rotate the pressure roller 23b fluctuates. That is, the value of the load torque of the pressure roller 23b (which is the torque received by the output gear 52 from the torsion spring 40 and is the minimum torque required to rotate the pressure roller 23b) fluctuates.

[0093] The spring constant of the torsion spring 40 is, for example, 0.01 kgf cm / °. In this case, if the load torque of the pressure roller 23b is 2 kgf cm, the pressure roller 23b will start rotating when the torsion spring 40 deflects 200° after the motor M starts. If the load torque of the pressure roller 23b is 3.5 kgf cm, the pressure roller 23b will start rotating when the torsion spring 40 deflects 350° after the motor M starts.

[0094] Even after the pressure roller 23b has started rotating, the torsion spring 40 continuously receives the driving force of the motor M and the load torque of the pressure roller 23b, causing the pressure roller 23b to begin rotating in a deflected state. The magnitude of the elastic force (i.e., restoring force) exerted by the torsion spring 40 on the output gear 52 is approximately proportional to the angular deflection of the torsion spring 40. That is, the torque corresponding to the angular deflection (i.e., deformation) of the torsion spring 40 is transmitted from the input gear 51 to the output gear 52. The product of the angular deflection when the pressure roller 23b rotates constantly and the spring constant of the torsion spring 40 is equivalent to the load torque of the pressure roller 23b.

[0095] Figures 2A to 2E The transfer state of the sheet S between the transfer clamping part Nt and the fixing clamping part Nf is shown. Figure 2AThis shows the state where the circumferential speed VB of the intermediate transfer belt 13 and the circumferential speed VF of the pressure roller 23b are equal. Figure 2B The state of the configuration according to the comparative example is shown, wherein the circumferential speed VF of the pressure roller 23b is 3% faster than the circumferential speed VB of the intermediate transfer belt 13. Figure 2C The state of the drive configuration according to this embodiment is shown, wherein the circumferential speed VF of the pressure roller 23b is 3% faster than the circumferential speed VB of the intermediate transfer belt 13. Figure 2D The state of the drive configuration according to this embodiment is shown, wherein the leading edge of the sheet S has reached the fixing clamping part Nf and the trailing edge of the sheet S has not yet left. Figure 2C The state is achieved through the transfer clamping part Nt. Figure 2E The state of the drive configuration according to this embodiment is shown, wherein the trailing edge of the sheet S has been from Figure 2D The state is achieved through the fixing clamping part Nf.

[0096] Comparison examples ( Figure 2B The configuration of the drive transmission unit DT in this comparative example differs from that in the present embodiment in that it is not equipped with a torsion spring 40. That is, according to this comparative example, it is equivalent to the drive transmission unit DT in the first embodiment. Figures 4A to 4C The input gear 51 and output gear 52 in the comparative example are configured to engage in a relatively non-rotatable manner. Except that it is not equipped with a torsion spring 40, the configuration of this comparative example is similar to that of this embodiment.

[0097] According to the design, even if the circumferential speed VF of the pressure roller 23b is set to match the circumferential speed VB of the intermediate transfer belt 13, Figure 2A The values ​​are equal due to reasons such as the thermal expansion mentioned above. Figure 2B The circumferential speed VF of the pressure roller 23b may also become faster than the circumferential speed VB of the intermediate transfer belt 13. If VF is faster than VB, then when the sheet S is held by both the transfer clamping part Nt and the fixing clamping part Nf, the distance that the pressure roller 23b attempts to convey the sheet S is longer than the distance that the sheet S is conveyed by the transfer clamping part Nt. Therefore, the sheet S may be pulled between the transfer clamping part Nt and the fixing clamping part Nf. In this case, based on the difference between the holding forces Ff and Ft, the sheet S may slide relative to the intermediate transfer belt 13.

[0098] According to this embodiment, by providing a torsion spring 40 on the drive transmission path from the motor M to the pressure roller 23b, the following configuration is achieved: drive is transmitted while allowing a delay in the angular velocity of the output gear 52 relative to the angular velocity of the input gear 51. That is, during the time period when the sheet S is held by both the transfer clamping part Nt and the fixing clamping part Nf, due to the deformation of the torsion spring 40, the state of the sheet S before it reaches the fixing clamping part Nf is different. Figure 2CCompared to this, the allowable circumferential speed VF of pressure roller 23b is slower. Figure 2D This allows for the absorption of the transfer amount deviation between the intermediate transfer belt 13 and the pressure roller 23b.

[0099] In this example, the general standard for the amount of transfer absorbed by the torsion spring 40 is set to 9 mm. This is because, when VF is 3% faster than VB, when the intermediate transfer belt 13 rotates a circumferential movement distance (297 mm) corresponding to the long side of the A4 size sheet, the pressure roller 23b rotates a circumferential movement distance (306 mm) that is approximately 9 mm larger than that of the intermediate transfer belt 13. However, in this description, the distance from the transfer clamping part Nt to the fixing clamping part Nf is ignored. Furthermore, the general standard for the amount of transfer deviation absorbed by the torsion spring 40 is not limited to 9 mm and can vary depending on the actual configuration of the image forming apparatus 100.

[0100] If the circumferential movement distance of the pressure roller 23b is shortened by 9 mm due to the deformation of the torsion spring 40, the slippage of the sheet S relative to the intermediate transfer belt 13 can be suppressed. If the diameter of the pressure roller 23b is 20 mm, it is sufficient to delay the rotation of the pressure roller 23b by approximately 50° in terms of its rotation angle. That is, compared to the case where the input gear 51 and output gear 52 rotate normally, allowing the input gear 51 and output gear 52 to rotate relative to each other results in a 50° smaller rotation of the pressure roller 23b.

[0101] As described above, when the pressure roller 23b rotates normally, the torsion spring 40 deflects at an angle corresponding to the load torque of the pressure roller 23b. Further deflection of the torsion spring 40 from this state allows for a delay in the rotation of the pressure roller 23b.

[0102] With the pressure roller 23b and output gear 52 arranged coaxially and rotating as a single unit, if the rotation of the pressure roller 23b is delayed by 50°, the rotation of the output gear 52 is also delayed by 50° relative to the input gear 51. That is, the output gear 52 rotates 50° relative to the input gear 51. Based on the deflection of the torsion spring 40 accompanying this relative rotation, the torsion spring 40 generates an additional torque. If the spring constant is 0.01 kgf cm / °, the additional torque generated by the torsion spring 40 accompanying the 50° rotation delay of the pressure roller 23b is 0.5 kgf cm.

[0103] That is, if the rotation of the pressure roller 23b is delayed by 50° due to the deformation of the torsion spring 40, a torque 0.5 kgf cm greater than the original load torque is applied to the pressure roller 23b. Therefore, if the diameter of the pressure roller 23b is set to 20 mm, then according to calculations, the maximum tension of 0.5 kgf ( Figure 2D Fft is applied to the sheet S.

[0104] In other words, such as Figure 2D As shown, while the sheet S is held by both the transfer clamping part Nt and the fixing clamping part Nf, the angle deflection of the torsion spring 40 gradually increases. Then, according to the increase in the angle deflection of the torsion spring 40, a tension Fft is generated on the sheet S between the transfer clamping part Nt and the fixing clamping part Nf, the maximum value of which is generally 0.5 kgf.

[0105] Meanwhile, according to the example above, the holding force of the sheet S at the transfer clamping part Nt is approximately 1 kgf, which is greater than the maximum value of the tension Fft appearing in the sheet S. Therefore, even if the angle deflection of the torsion spring 40 increases while the sheet S is clamped by both the transfer clamping part Nt and the fixing part Nf, slippage of the sheet S relative to the intermediate transfer belt 13 can be prevented, and image defects can be prevented.

[0106] After that, as Figure 2E As shown, when the trailing edge of sheet S passes through the transfer clamping part Nt, sheet S is released from tension Fft, and the angle deflection of the torsion spring 40 begins to decrease. That is, in Figure 2D In this state, the torsion spring 40 deflects and deforms at such an angle that the torque applied to the output gear 52 by the elastic force of the torsion spring 40 is balanced by the sum of the original load torque of the pressure roller 23b and the torque applied to the pressure roller 23b by the tension Fft from the sheet S. Simultaneously, in Figure 2E In this state, the angle deflection of the torsion spring 40 is reduced to such an angle deflection that the torque applied to the output gear 52 by the elastic force of the torsion spring 40 is balanced with the load torque of the pressure roller 23b.

[0107] Therefore, when the trailing edge of the sheet S passes the transfer clamping part Nt, the pressure roller 23b temporarily moves at a circumferential speed VF (before the leading edge of the sheet S reaches the fixing clamping part Nf) higher than that of the sheet S. Figure 2C ( ) Fast circumferential speed VF rotation.

[0108] Reference Figures 5A to 5C The description covers the variation of the angular velocity of the element involved in the drive transmission from motor M to pressure roller 23b according to this embodiment.

[0109] Figure 5A Corresponding to Figure 2C It shows the state after the leading edge of the sheet S has passed the transfer clamping part Nt and before the leading edge of the sheet S reaches the fixing clamping part Nf. Figure 5B Corresponding to Figure 2D It shows the state after the leading edge of the sheet S reaches the fixing clamping part Nf and before the trailing edge of the sheet S has passed the transfer clamping part Nt. Figure 5C Corresponding to Figure 2E It shows the state after the trailing edge of the sheet S has passed through the transfer clamping part Nt and before the trailing edge of the sheet S has passed through the fixing clamping part Nf.

[0110] exist Figures 5A to 5C In this diagram, the angular velocity of the output shaft of motor M is referred to as RM, and the angular velocity of pressure roller 23b is referred to as RR. The angular velocity of the input side (i.e., arm portion 40a) of torsion spring 40 is referred to as RT1, and the angular velocity of the output side (i.e., arm portion 40b) of torsion spring 40 is referred to as RT2. The angular velocity RT1 of the input side of torsion spring 40 is determined based on the angular velocity RM of the output shaft of motor M and the reduction ratio of the drive transmission mechanism DT1 from the output shaft of motor M to the input gear 51. The angular velocity RR of pressure roller 23b is determined based on the angular velocity RT2 on the output side of torsion spring 40 and the reduction ratio of the drive transmission mechanism DT2 from the output gear 52 to the pressure roller 23b.

[0111] like Figure 5A As shown, before the leading edge of the sheet S reaches the fixing clamping part Nf Figure 2C In this state, the angular velocity RT2 on the output side of the torsion spring 40 is equal to the angular velocity RT1 on the input side.

[0112] like Figure 5B As shown, the sheet S is held by both the transfer clamping part Nt and the fixing clamping part Nf. Figure 2D In the state of, with Figure 5A Compared to the previous state, the angular velocity RR of the pressure roller 23b is delayed by, for example, 3%. Furthermore, due to the elastic deformation of the torsion spring 40, the angular velocity RT2 on the output side of the torsion spring 40 is allowed to be delayed by, for example, 3% compared to the angular velocity RT1 on the input side of the torsion spring 40. In this state, the output gear 52 rotates at a slower speed than the input gear 51. That is, due to the elastic deformation of the torsion spring 40, the circumferential speed difference between the pressure roller 23b and the intermediate transfer belt 13 is absorbed.

[0113] In the first state (where the pressure roller 23b and the intermediate transfer belt 13 are driven by the motor M and the sheet S is separated from at least one of the outer peripheral surface 23b1 (i.e., the first contact surface) of the pressure roller 23b and the outer peripheral surface 13a (i.e., the second contact surface) of the intermediate transfer belt 13), the circumferential speed of the outer peripheral surface 23b1 of the pressure roller 23b is referred to as the first speed. Similarly, the circumferential speed of the outer peripheral surface 13a of the intermediate transfer belt 13 is referred to as the second speed. The second speed is different from the first speed. For example, in Figure 2C In the state shown, the circumferential speed VF (i.e., the first speed) of the outer peripheral surface 23b1 of the pressure roller 23b is a different speed from the circumferential speed VB (i.e., the second speed) of the outer peripheral surface 13a of the intermediate transfer belt 13. In this case, as... Figure 2D As shown, in the state where the pressure roller 23b and the intermediate transfer belt 13 are driven by the motor M and the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13 (second state), the torsion spring 40 deforms. Due to this deformation, the torsion spring 40 allows the circumferential velocity VF of the outer peripheral surface 23b1 of the pressure roller 23b to be greater than... Figure 2C The speed shown in the state (i.e., the first speed) is closer to the circumferential speed VB of the outer peripheral surface 13a of the intermediate transfer belt 13 (i.e., the second speed) and the circumferential speed (i.e., the third speed). That is, the difference between the third speed and the second speed is less than the difference between the first speed and the second speed. The third speed can be equal to the second speed. Therefore, it becomes possible to suppress... Figure 2C The speed difference between the outer peripheral surface 23b1 of the pressure roller 23b and the outer peripheral surface 13a of the intermediate transfer belt 13 under the condition affects the conveying stability of the sheet S.

[0114] The position where the sheet S and the intermediate transfer belt 13 come into contact is called the contact position. When the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13, the deformation of the torsion spring 40 maintains a state where the difference between the moving speed of the sheet S at the contact position and the circumferential speed VB of the outer peripheral surface 13a of the intermediate transfer belt 13 (i.e., the first speed difference) is less than the difference between the circumferential speed VF of the outer peripheral surface 23b1 of the pressure roller 23b and the circumferential speed VB of the outer peripheral surface 13a of the intermediate transfer belt 13 (i.e., the second speed difference). In other words, the relative sliding between the sheet S and the intermediate transfer belt 13 at the transfer clamping part Nt is maintained at least less than the difference between the circumferential speed VF of the outer peripheral surface 23b1 of the pressure roller 23b and the circumferential speed VB of the outer peripheral surface 13a of the intermediate transfer belt 13. In other words, the sheet conveying device is configured such that the first speed difference is less than the second speed difference when the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13 by the deformation of the torsion spring 40.

[0115] like Figure 5C As shown, after the trailing edge of sheet S has passed through the transfer clamping part Nt... Figure 2E Under these conditions, the angular velocity RR of the pressure roller 23b becomes greater than... Figure 5A The state is fast. Furthermore, the angular velocity RT2 on the output side of the torsion spring 40 becomes faster than the angular velocity RT1 on the input side of the torsion spring 40. This is because when the trailing edge of the sheet S has passed through the transfer clamping part Nt and the tension is released, a portion of the elastic deformation of the torsion spring 40 recovers, causing the output side of the torsion spring 40 to temporarily rotate faster than the input side. In this state, the output gear 52 rotates faster than the input gear 51. Furthermore, if the angular deflection of the torsion spring 40 becomes equal to... Figure 5AUnder normal conditions, the angular velocity RR of the pressure roller 23b and the angular velocity RT2 on the output side of the torsion spring 40 will be equal to... Figure 5A The state.

[0116] In the above description, an example was given of a case where the pressure roller 23b rotates at a circumferential speed 3% faster than the intermediate transfer belt 13 due to thermal expansion. However, even when the speed difference between the pressure roller 23b and the intermediate transfer belt 13 is approximately 0.5%, a conveying amount deviation of 0.5 mm will occur if the sheet S is conveyed 100 mm while being held by both the transfer clamping part Nt and the fixing clamping part Nf. Even with such a relatively small conveying amount deviation, slippage of the sheet S relative to the intermediate transfer belt 13 may occur, resulting in image defects. That is, even when the speed difference between the pressure roller 23b and the intermediate transfer belt 13 is relatively small, the configuration of the torsion spring 40 according to this embodiment is useful.

[0117] Based on the above description, the thermal expansion of the pressure roller 23b is shown as the cause of the circumferential speed difference between the pressure roller 23b and the intermediate transfer belt 13, but the cause of the circumferential speed difference is not limited to this. For example, the circumferential speed difference between the pressure roller 23b and the intermediate transfer belt 13 may be caused by wear on the outer peripheral portion of the belt drive roller 14. Even in this case, the configuration of the torsion spring 40 of this embodiment is useful.

[0118] The following is a summary of the above configuration. If the unloaded state of the torsion spring 40 is referred to as the free state, then while the input gear 51 rotates under the driving force of the motor M, the torsion spring 40 will be in a deformed state, deforming from the free state. In this state, the torsion spring 40 is deformed within the elastic region. In other words, even if the angular velocity RR of the pressure roller 23b is constant, the torsion spring 40 will still be deformed within the elastic region while the pressure roller 23b rotates. In this state, the torsion spring 40 is capable of elastic deformation towards the downstream and upstream sides in the rotational direction of the input gear 51.

[0119] For example, when sheet S is held by both the transfer clamping part Nt and the fixing clamping part Nf. Figure 2D In this state, while the driving force of the motor M is input to the input gear 51, the angular velocity of the output gear 52 is slower than that of the input gear 51. According to the drive transmission unit DT of this embodiment, by deforming the torsion spring 40 when the angular velocity of the output gear 52 is slower than that of the input gear 51 while the driving force of the motor M is input to the input gear 51, the pressure roller 23b is allowed to rotate.

[0120] For example, after the trailing edge of sheet S has passed through the transfer clamping part Nt Figure 2E In this state, while the driving force of the motor M is input to the input gear 51, the angular velocity of the output gear 52 is faster than that of the input gear 51. According to the drive transmission unit DT of this embodiment, the pressure roller 23b is allowed to rotate when the driving force of the motor M is input to the input gear 51 and the angular velocity of the output gear 52 is faster than that of the input gear 51.

[0121] Advantages of this embodiment

[0122] As described above, due to the elastic deformation of the torsion spring 40 (i.e., the elastic member), drive transmission from the motor M to the pressure roller 23b (i.e., the first conveying member) is allowed when the angular velocity of the output gear 52 (i.e., the second rotating member) is different from the angular velocity of the input gear 51 (i.e., the first rotating member). In other words, the torsion spring 40 (i.e., the elastic member) can deform to allow the pressure roller 23b (i.e., the first conveying member) to rotate when the angular velocities of the input gear 51 (i.e., the first rotating member) driven by the motor M and the output gear 52 (i.e., the second rotating member) are different from each other. The sheet conveying device according to this embodiment is configured to allow the driving force of the drive source to be transmitted to the first conveying member when the angular velocity of the second rotating member is slower than that of the first rotating member by the deformation of the elastic member. Furthermore, the sheet conveying device according to this embodiment is configured to allow the driving force of the drive source to be transmitted to the first conveying member when the angular velocity of the second rotating member is faster than that of the first rotating member.

[0123] With this configuration, when there is a circumferential speed difference between the pressure roller 23b (i.e., the first conveying member) and the intermediate transfer belt 13 (i.e., the second conveying member), the torsion spring 40 elastically deforms when the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13. This allows the pressure roller 23b to rotate at a circumferential speed corresponding to the circumferential speed of the intermediate transfer belt 13. Consequently, defects caused by slackness or pulling of the sheet S between the pressure roller 23b and the intermediate transfer belt 13 can be suppressed.

[0124] That is, according to this embodiment, a sheet conveying device and an image forming device that can convey sheet material more stably can be provided.

[0125] As a method for suppressing the speed difference between the pressure roller 23b and the intermediate transfer belt 13, techniques for suppressing the relaxation (i.e., circulation) of the sheet S between the transfer clamping section Nt and the fixing clamping section Nf are known. However, in order to control the circulation, it is necessary to provide a sensor for detecting the circulation and two independent drive systems for driving the fixing unit and the transfer unit respectively, which increases the cost. In contrast, according to this embodiment, a sheet transport device and an image forming device that can transport the sheet more stably with a simpler configuration can be provided.

[0126] Furthermore, according to this embodiment, if the sheet S remains in contact with both the pressure roller 23b and the intermediate transfer belt 13, the phase difference (i.e., the positional deviation in the rotational direction) between the output gear 52 and the input gear 51 increases. As a result, the angular deflection (i.e., the amount of deformation) of the torsion spring 40 changes continuously while the sheet S remains in contact with both the pressure roller 23b and the intermediate transfer belt 13. Figure 2D In other words, the sheet conveying device of this embodiment, including the torsion spring 40, is configured such that the angle deflection (i.e., the amount of deformation) of the torsion spring 40 changes continuously while the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13.

[0127] The state in which the sheet S is held by the intermediate transfer belt 13 and the secondary transfer roller 22, and also by the pressure roller 23b and the fixing film assembly 23a, is called the double-clamping state or simply the clamping state for ease of description. Furthermore, the position of the sheet S when the clamping state is released after the start of the double-clamping state, that is, the position of the sheet S when the double-clamping state ends, is called the release position or the end position. The state in which the angular velocities of the input gear 51 and the output gear 52 are different from each other is called the different-velocity state. According to this embodiment, when the sheet S reaches the release position, the state in which the sheet S is clamped by the intermediate transfer belt 13 and the secondary transfer roller 22 terminates. That is, the trailing edge of the sheet S has passed through the transfer clamping section Nt.

[0128] The torsion spring 40 is deformable such that after the initiation of different speed states, the different speed states persist until at least the sheet S reaches the release position. In other words, the torsion spring 40 is deformable such that when the sheet S reaches the release position, the input gear 51 and the output gear 52 are in different speed states. More specifically, the torsion spring 40 is deformable such that when the sheet S reaches the release position, the angular velocity of the output gear 52 is slower than the angular velocity of the input gear 51. In other words, the torsion spring 40 allows the state where the angular velocity of the output gear 52 is slower than the angular velocity of the input gear 51 when the sheet S reaches the release position. Furthermore, after the sheet S passes the release position, the state where the angular velocities of the input gear 51 and the output gear 52 are different from each other persists until the deformation of the torsion spring 40 is restored. Now, the sheet with the longest length in the conveying direction of the sheet S among the sheets that can be stored in the feed tray 19 is called the longest sheet. The torsion spring 40 is configured such that the deformation amount increases until the trailing edge of the longest sheet separates from the intermediate transfer belt 13. The torsion spring 40 is deformable such that when the longest sheet is conveyed as sheet S and a different speed state begins, the different speed state continues until at least sheet S reaches the release position.

[0129] As described above, with respect to the direction of the rotation axis Ax, the arm portion 40a and the spring hook portion 51a are arranged away from the arm portion 40b and the spring hook portion 52a. Furthermore, with respect to the direction of the rotation axis Ax, the input gear 51 and the output gear 52 are arranged away from each other. Moreover, the torsion spring 40 is a torsion helical spring configured to deflect around the rotation axis Ax. Based on these configurations, the number of turns of the torsion spring 40 can be increased, and as a result, the spring constant of the torsion spring 40 can be reduced. That is, the state of continuously changing deformation of the torsion spring 40 (i.e., different speed states) can continue until the sheet S reaches the release position. As a result, according to this embodiment, it becomes possible to suppress the increase in the restoring force of the torsion spring 40 relative to the holding force of the sheet S at the transfer clamping portion Nt.

[0130] By deforming the torsion spring 40, the difference between the circumferential velocity VF of the outer peripheral surface 23b1 of the pressure roller 23b and the circumferential velocity VB of the outer peripheral surface 13a of the intermediate transfer belt 13 becomes smaller than the difference between the circumferential velocity VF of the outer peripheral surface 23b1 of the pressure roller 23b and the circumferential velocity VB of the outer peripheral surface 13a of the intermediate transfer belt 13 when the sheet S is separated from at least one of the pressure roller 23b and the intermediate transfer belt 13. In this embodiment, when the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13, the deformation of the torsion spring 40 allows the pressure roller 23b to rotate continuously at a speed corresponding to the circumferential velocity VB of the intermediate transfer belt 13 (that is, the third speed).

[0131] The pressure roller 23b (i.e., the first conveying member) is arranged downstream of the intermediate transfer belt 13 (i.e., the second conveying member) in the sheet conveying direction. Furthermore, in a state where the sheet S is separated from at least one of the pressure roller 23b and the intermediate transfer belt 13 ( Figure 2C The circumferential speed VF (i.e., the first speed) of the pressure roller 23b is faster than the circumferential speed VB (i.e., the second speed) of the intermediate transfer belt 13. In this case, according to the comparative example without the torsion spring 40, even when the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13, as... Figure 2B As shown, the circumferential speed VF of the pressure roller 23b is also maintained, and tension is applied to the sheet S. This tension may cause the sheet S to slip relative to the intermediate transfer belt 13, which may lead to image defects.

[0132] Conversely, according to this embodiment, due to the deformation of the torsion spring 40, that is, the deformation of the elastic member, when the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13, as Figure 2D As shown, the circumferential speed VF of the pressure roller 23b decreases. That is, the circumferential speed VF of the pressure roller 23b becomes slower than... Figure 2C The slower speed, also known as the third speed, is achieved when the sheet S is in contact with both the pressure roller 23b and the intermediate transfer belt 13. This prevents image defects caused by tension applied to the sheet S.

[0133] Example of driver delivery path configuration

[0134] Reference Figure 3A and Figure 3B The description includes a configuration example of the drive transmission path for the torsion spring 40. The following will describe... Figure 3C The modified example shown is a collection of mechanical elements that connect the motor M, which serves as the drive source, and the drive target (i.e., the load or driven component, such as the pressure roller 23b) so that the driving force of the motor M (i.e., the rotational torque generated by the motor M) is transmitted from the motor M to the drive target.

[0135] Figure 3A This is a schematic diagram illustrating the drive transmission path in the image forming apparatus 100 according to the first embodiment. The pressure roller 23b is connected to the motor M via a drive transmission unit DT including a torsion spring 40. Furthermore, the belt drive roller 14 is connected to the motor M without the drive transmission unit DT. Additionally, the drive roller of the sheet discharge roller pair 24 (i.e., the sheet discharge roller 24a) is connected to the motor M via the drive transmission unit DT. Therefore, the intermediate transfer belt 13, the pressure roller 23b, and the sheet discharge roller pair 24 are driven to rotate by the motor M.

[0136] According to the first embodiment, even if the circumferential speeds of the pressure roller 23b and the intermediate transfer belt 13 do not correspond due to the thermal expansion of the rollers, as described above, this speed difference can be absorbed by the deformation of the torsion spring 40. Thus, slippage of the sheet S relative to the intermediate transfer belt 13 can be suppressed.

[0137] Furthermore, the configuration in which the drive roller 14 and the pressure roller 23b are driven by the same motor M as according to the first embodiment has the following advantages. Assuming that the torsion spring 40 has deformed and tension Fft is applied to the sheet S between the transfer clamping part Nt and the fixing clamping part Nf, as... Figure 2D As shown. In this state, at the fixing clamping part Nf, a torque is applied from the sheet S to the pressure roller 23b in the opposite direction to the driving direction of the pressure roller 23b due to the tension Fft of the sheet S. That is, the apparent load torque of the pressure roller 23b increases.

[0138] Simultaneously, at the transfer clamping part Nt, a torque is applied from the sheet S to the intermediate transfer belt 13 in the direction of rotation of the belt drive roller 14 due to the tension of the sheet S. That is, the apparent load torque of the belt drive roller 14 is reduced.

[0139] Therefore, on the output shaft of motor M, the changes in the apparent load torque of pressure roller 23b and the apparent load torque of drive roller 14 are offset by the tension Fft. Thus, compared to the case where the changes in the apparent load torque of pressure roller 23b and drive roller 14 are not offset, the sheet S can be stably conveyed by using an inexpensive motor M with a relatively small rated output.

[0140] Furthermore, the torsion spring 40 has greater flexibility than gears typically made of metal or engineering plastics (such as polyacetal) and serves to dampen high-frequency band vibrations. By inserting the torsion spring 40 in the drive transmission path from the motor M to the pressure roller 23b, high-frequency band vibrations between components in the drive transmission path between the motor M and the pressure roller 23b can be damped. For example, rotational vibrations of the gear inserted between the motor M and the input gear 51 of the drive transmission unit DT are less likely to be transmitted to the pressure roller 23b.

[0141] Figure 3B This is a schematic diagram illustrating the drive transmission path in an image forming apparatus according to a modified example. The drive rollers of the pressure roller 23b and the sheet discharge roller pair 24 (i.e., the sheet discharge roller 24a) are connected to the motor M via a drive transmission unit DT including a torsion spring 40. Meanwhile, the drive roller 14 is connected to a motor M1, which is different from the motor M that drives the pressure roller 23b.

[0142] According to Figure 3BAs in the modified example, even when the drive roller 14 is driven by a drive source (i.e., motor M1) independent of the drive source (i.e., motor M) of the pressure roller 23b, there may still be a circumferential speed difference between the pressure roller 23b and the intermediate transfer belt 13. In this case, the circumferential speed difference can be absorbed by the deformation of the torsion spring 40, and similar advantages as in the first embodiment can be obtained.

[0143] Example of modifying a torsion spring

[0144] The following modification example can be provided as a configuration that can further suppress the slippage of the sheet S relative to the intermediate transfer belt 13.

[0145] First, consider reducing the spring constant of the torsion spring 40. The smaller the spring constant of the torsion spring 40, the greater the angular deflection of the torsion spring 40 caused by the circumferential speed difference between the intermediate transfer belt 13 and the pressure roller 23b. Figure 2D The smaller the tension Fft applied to the sheet S under the condition of [condition], the lower the stress Fft. However, a torsion spring 40 with a small spring constant may easily cause its angle deflection to increase, and may generate torsional stress exceeding the maximum allowable stress. Therefore, it is preferable to determine the spring constant by taking into account the maximum value of the torque load of the pressure roller 23b and the maximum value of the conveying amount deviation between the intermediate transfer belt 13 and the pressure roller 23b.

[0146] From the state where the leading edge of the sheet S contacts the pressure roller 23b to the state where the trailing edge of the sheet S separates from the pressure roller 23b, the maximum value of the angle deflection (i.e., deformation) of the torsion spring 40 can preferably be within 30% of the angle deflection (i.e., deformation) corresponding to the maximum allowable stress of the torsion spring 40. As a result, at least when the sheet S reaches the release position, the angle deflection (i.e., deformation) of the torsion spring 40 will be within 30% of the angle deflection (i.e., deformation) corresponding to the maximum allowable stress of the torsion spring 40. In other words, the drive transmission path of the sheet conveying device can preferably be configured such that the maximum value of the angle deflection during the aforementioned time period falls within 30% of the angle deflection corresponding to the maximum allowable stress of the torsion spring 40. The torsion spring 40 can deform in the direction of increasing deformation when the trailing edge of the longest sheet has reached the transfer clamping part Nt. Even when conveying the longest sheet, the relationship between the maximum value of the angle deflection of the torsion spring 40 and the angle deflection corresponding to the maximum allowable stress of the torsion spring 40 can preferably be satisfied.

[0147] Methods for reducing the stress applied to the spring wire of the torsion spring 40 include changing the material of the spring wire, increasing the wire diameter, or increasing the number of turns or the winding diameter. Increasing the wire diameter increases the spring constant, making it preferable to adjust the stress by changing the material, number of turns, or winding diameter. That is, if the stress applied to the spring wire is reduced by changing the configuration of the torsion spring 40 itself, the size or cost of the torsion spring 40 may increase.

[0148] Example of using multiple torsion springs

[0149] To prevent an increase in the size or cost of the torsion spring 40, multiple torsion springs, i.e. multiple elastic components, can be used. Figures 6A to 6D as well as Figure 7A and Figure 7B Modification examples using multiple torsion springs are shown respectively. According to... Figures 6A to 7B The various modified examples, compared to the first embodiment, can suppress the stress applied to each torsion spring.

[0150] According to Figure 6A and Figure 6B In the modified example, the first torsion springs 40j and 40c are referred to as the first elastic members, and the second torsion springs 40k and 40d are examples of the second elastic members. According to these examples, the second torsion springs 40k and 40d are arranged in parallel with the first torsion springs 40j and 40c in the transmission path of the driving force from the drive source to the pressure roller 23b.

[0151] Figure 6A A modified example of multiple torsion springs arranged in parallel is shown, wherein a second torsion spring 40k is disposed inside a first torsion spring 40j. The first torsion spring 40j and the second torsion spring 40k engage with an input gear 51 and an output gear 52, respectively. A portion of the driving force transmitted from the motor M to the input gear 51 is transmitted to the output gear 52 via the first torsion spring 40j, and another portion of the driving force is transmitted to the output gear 52 via the second torsion spring 40k.

[0152] Figure 6BThis is a modified example of multiple torsion springs arranged in parallel, wherein the first torsion spring 40c and the second torsion spring 40d rotate about different axes of rotation. The driving force of the motor M is fed to the first input gear 51-1 and the second input gear 51-2 via the drive transmission member 56. Furthermore, the first output gear 52-1 and the second output gear 52-2 are connected to the pressure roller 23b via the drive transmission member 57. The first torsion spring 40c engages with the first input gear 51-1 and the first output gear 52-1. The second torsion spring 40d engages with the second input gear 51-2 and the second output gear 52-2. A portion of the driving force transmitted from the motor M to the input-side drive transmission member 56 is transmitted to the output-side drive transmission member 57 via the first torsion spring 40c. Another portion of the driving force transmitted from the motor M to the input-side drive transmission member 56 is transmitted to the output-side drive transmission member 57 via the second torsion spring 40d.

[0153] Figure 7A This illustrates the case where multiple torsion springs are arranged in parallel (e.g.) Figure 6A and Figure 6B (The following is a schematic diagram of the drive transmission path from motor M to pressure roller 23b.) According to this modified example, if there is a circumferential speed difference between pressure roller 23b and intermediate transfer belt 13, each of the plurality of torsion springs elastically deforms to allow for a delay in the angular velocity RR of pressure roller 23b. Therefore, slippage of sheet S relative to intermediate transfer belt 13 can be suppressed.

[0154] According to Figure 6C and Figure 6D In the modified example, the first torsion springs 40e and 40g are referred to as the first elastic members, and the second torsion springs 40f and 40h are examples of the second elastic members. According to these examples, the second torsion springs 40f and 40h are arranged in series with the first torsion springs 40e and 40g in the transmission path of the driving force from the drive source to the pressure roller 23b.

[0155] Figure 6C A modified example of a series arrangement of multiple torsion springs is shown, wherein a second torsion spring 40f is disposed inside a first torsion spring 40e. The first torsion spring 40e engages with an input gear 51 and an intermediate gear 58. The second torsion spring 40f engages with an intermediate gear 58 and an output gear 52. The driving force transmitted from the motor M to the drive transmission member 56 is transmitted via the first torsion spring 40e to the intermediate gear 58, and further via the second torsion spring 40f to the output gear 52.

[0156] Figure 6DA modified example of a series arrangement of multiple torsion springs is shown, wherein a first torsion spring 40g and a second torsion spring 40h are arranged to rotate about mutually different axes of rotation. The first torsion spring 40g engages with the input gear 51 and the first intermediate gear 58a. The second torsion spring 40h engages with the second intermediate gear 58b and the output gear 52. The first intermediate gear 58a engages with the second intermediate gear 58b. The driving force transmitted from the motor M to the input gear 51 is transmitted via the first torsion spring 40g to the first intermediate gear 58a, and further via the second torsion spring 40h to the output gear 52.

[0157] Figure 7B This illustrates the case where multiple torsion springs are arranged in series (as per...). Figure 6C and Figure 6D (The following is a schematic diagram of the drive transmission path from motor M to pressure roller 23b.) According to this modified example, if there is a circumferential speed difference between pressure roller 23b and intermediate transfer belt 13, each of the plurality of torsion springs elastically deforms to allow for a delay in the angular velocity RR of pressure roller 23b. Therefore, slippage of sheet S relative to intermediate transfer belt 13 can be suppressed.

[0158] Example of using torque limiters in combination

[0159] Reference Figure 8A and Figure 8B as well as Figures 9A to 9C Describe an example of the combined use of a torsion spring (i.e., an elastic member) and a torque limiter.

[0160] exist Figure 8A and Figure 8B In the example shown, the torsion spring 40m and the torque limiter 41 are arranged in parallel. The torque limiter 41 includes a first rotating portion 41a and a second rotating portion 41b. The torque limiter 41 is configured to rotate integrally when the rotational load between the first rotating portion 41a and the second rotating portion 41b is equal to or less than a predetermined torque value, and to allow relative rotation of the first rotating portion 41a and the second rotating portion 41b when the rotational load exceeds the torque value.

[0161] exist Figure 8A In the example, the driving force of the motor M is distributed to the input gear 51 and the first rotating portion 41a of the torque limiter 41 via the input-side drive transmission member 56. The torque transmitted from the input gear 51 to the output gear 52 via the torsion spring 40m and the torque transmitted from the first rotating portion 41a of the torque limiter 41 to the second rotating portion 41b are transmitted to the pressure roller 23b via the output-side drive transmission member 57.

[0162] exist Figure 8BIn the example, the driving force of motor M2, independent of motor M connected to torsion spring 40m, enters the first rotating portion 41a of torque limiter 41. The torque transmitted from input gear 51 to output gear 52 via torsion spring 40m and the torque transmitted from the first rotating portion 41a of torque limiter 41 to second rotating portion 41b are transmitted to pressure roller 23b via output-side drive transmission member 57.

[0163] for Figure 8A and Figure 8B Both examples share the characteristic that the torque limiter 41 is set to a value less than the load torque of the pressure roller 23b. When a drive target other than the pressure roller 23b is also driven via the drive transmission member 57, the torque limiter 41 is set to a value less than the load torque including that drive target. Furthermore, drive transmission mechanisms DT3 and DT4 ( Figure 9A The reduction ratio is set such that the angular velocity of the first rotating portion 41a of the torque limiter 41 becomes faster than the angular velocity of the second rotating portion 41b when the pressure roller 23b rotates at a constant speed. The drive transmission mechanism DT3 is the drive transmission path from the output shaft of the motor M to the first rotating portion 41a of the torque limiter 41, and the drive transmission mechanism DT4 is the drive transmission path from the second rotating portion 41b of the torque limiter 41 to the pressure roller 23b.

[0164] By employing a configuration where the motor M side (i.e., the first rotating portion 41a) of the torque limiter 41 rotates faster than the pressure roller 23b side (i.e., the second rotating portion 41b), the torque limiter 41 normally slips when the pressure roller 23b rotates at a constant speed. Therefore, a stable torque can be transmitted to the pressure roller 23b via the torque limiter 41. The torque limiter 41 alone cannot rotate the pressure roller 23b, but a portion of the torque used to drive the pressure roller 23b can be carried on the torque limiter 41. That is, the torque loaded on the torsion spring 40m can be reduced, and the stress applied to the torsion spring 40m can also be reduced.

[0165] Reference Figures 9A to 9C Describe the change in angular velocity of the element involved in the drive transmission from motor M to pressure roller 23b according to this modified example. Figures 9A to 9C Each corresponds to Figures 2C to 2E The state.

[0166] like Figure 9A As shown, before the leading edge of the sheet S reaches the fixing clamping part Nf Figure 2CIn this state, the angular velocity RT2 on the output side of the torsion spring 40m is equal to the angular velocity RT1 on the input side. Furthermore, the angular velocity RT4 on the output side of the torque limiter 41 (i.e., the second rotating portion 41b) is slower than the angular velocity RT3 on the input side (i.e., the first rotating portion 41a). In this example, with RT3 at 100%, RT4 is set to 99%. Additionally, by transmitting drive from the torque limiter 41 to the pressure roller 23b via the drive transmission mechanism DT4, a torque TF1 corresponding to the torque value TT of the torque limiter 41 and the reduction ratio of the drive transmission mechanism DT4 is transmitted to the pressure roller 23b. The torque TF1 carried on the torque limiter 41 is less than the load torque TF of the pressure roller 23b. The torque TF2 carried on the torsion spring 40m corresponds to (TF-TF1).

[0167] like Figure 9B As shown, the sheet S is held by both the transfer clamping part Nt and the fixing clamping part Nf. Figure 2D Under these conditions, the angular velocity RR of the pressure roller 23b is, for example, greater than... Figure 9A The state is 3% slower. The angular velocity RT2 on the output side of the torsion spring 40m is, for example, 3% slower than the angular velocity RT1 on the input side of the torsion spring 40m. This is because, as described above, the circumferential speed difference between the pressure roller 23b and the intermediate transfer belt 13 is absorbed by the increase in the angular deflection of the torsion spring 40m. The angular velocity RT4 on the output side of the torque limiter 41 (that is, the second rotating part 41b) is also delayed, but the torque TF2 transmitted to the pressure roller 23b via the torque limiter 41 is... Figure 9A The states are the same.

[0168] like Figure 9C As shown, the trailing edge of sheet S has already passed through the transfer clamping part Nt. Figure 2E Under these conditions, the angular velocity RR of pressure roller 23b is greater than that of pressure roller 23b. Figure 9A The state is fast. In addition, the angular velocity RT2 on the output side of the torsion spring 40m is faster than the angular velocity RT1 on the input side of the torsion spring 40m. This is because when the trailing edge of the sheet S has passed through the transfer clamping part Nt and the tension is released, the angular deflection of the torsion spring 40m decreases, causing the output side of the torsion spring 40m to rotate faster than the input side temporarily.

[0169] If the rotational speed of the pressure roller 23b becomes too fast, it may affect the fixing performance. According to this modified example, if the angular velocity RT4 of the output side of the torque limiter 41 (i.e., the second rotating portion 41b) becomes faster than the angular velocity RT3 of the input side (i.e., the first rotating portion 41a), a braking force is generated to suppress the rapid acceleration of the pressure roller 23b. When the sheet material in contact with the pressure roller 23b (i.e., the first conveying member) separates from the pressure roller 23b, the torque limiter 41 suppresses the acceleration of the pressure roller 23b by the restoring force of the torsion spring 40 (i.e., the elastic member). That is, by combining the torque limiter 41 and the torsion spring 40, the rotational speed of the pressure roller 23b can be further stabilized, and more stable fixing performance can be achieved.

[0170] Example of using rotating dampers in combination

[0171] As a method for stabilizing the rotational speed of the pressure roller 23b, a torsion spring 40 and a rotational damper 45 can be used in combination, such as... Figure 3C As shown. The rotary damper 45 includes an input-side rotating portion 45a and an output-side rotating portion 45b, and a fluid such as oil is filled between the input-side rotating portion 45a and the output-side rotating portion 45b. When the input-side rotating portion 45a and the output-side rotating portion 45b rotate relative to each other, the rotary damper 45 generates a braking force corresponding to the speed of the relative rotation.

[0172] According to the example shown in the figure, the input gear 51 of the drive transmission unit DT engages with the input side rotating portion 45a of the rotary damper 45, and the output gear 52 of the drive transmission unit DT engages with the output side rotating portion 45b of the rotary damper 45.

[0173] If there is a circumferential speed difference between the intermediate transfer belt 13 and the pressure roller 23b, a speed difference will occur between the input gear 51 and the output gear 52 when the sheet S is held by both the transfer clamping part Nt and the fixing clamping part Nf, resulting in relative rotation between the input-side rotating part 45a and the output-side rotating part 45b. However, in this state, the speed difference between the input gear 51 and the output gear 52 is very small, and the relative rotational speed between the input-side rotating part 45a and the output-side rotating part 45b is also very small, resulting in a very small braking force generated by the rotation damper 45.

[0174] Meanwhile, when the trailing edge of the sheet S has passed the transfer clamping part Nt, if the pressure roller 23b attempts to rotate at high speed by the elastic force of the torsion spring 40, the speed difference between the input gear 51 and the output gear 52 increases. In this case, the relative rotational speed of the input-side rotating part 45a and the output-side rotating part 45b increases, and the braking force generated by the rotation damper 45 increases. As a result, the rapid acceleration of the pressure roller 23b can be suppressed, and more stable fixing can be achieved.

[0175] Example of assembling a torsion spring in a pre-torsional state

[0176] An assembly example of assembling the torsion spring 40 into the device in a pre-torsional state will be described. As described above, according to the first embodiment, the torsion spring 40 begins to deflect after the motor M is started, and the output gear 52 and the pressure roller 23b begin to rotate when the torque transmitted from the deflected torsion spring 40 to the output gear 52 exceeds the load torque of the pressure roller 23b. That is, from the start of the motor M until the pressure roller 23b begins to rotate, a delay time is generated until the angle deflection of the torsion spring 40 reaches a sufficient value.

[0177] Reference Figure 10 The description describes a modified example of assembling the torsion spring 40 onto the device in a state of pre-torsional deflection at a predetermined angle, as a method to reduce the delay time before the start of rotation of the pressure roller 23b. Figure 10 This is an exploded view of the drive transfer unit DT based on this modified example.

[0178] like Figure 10 As shown, according to this modified example, protrusions 51d and 52d are formed on the input gear 51 and the output gear 52. With the torsion spring 40, input gear 51, and output gear 52 assembled, the protrusions 51d and 52d engage with each other and limit the relative rotation angle (i.e., rotation phase) of the input gear 51 and the output gear 52 about the rotation axis Ax in the rotational direction. In this state, with the unloaded state set as a reference, the torsion spring 40 remains pre-deflected by a predetermined angle T1. That is, when the input gear 51 is stopped, the torsion spring 40 remains deformed from the unloaded state. The torsional direction of the angle deflection T1 is set such that a torque in the same direction as the torque transmitted from the torsion spring 40 to the output gear 52 when the pressure roller 23b is driven to rotate is applied from the torsion spring 40 to the output gear 52.

[0179] The predetermined angle deflection T1 is set to be less than the total load torque of the drive target transmitted to it via the torsion spring 40. For example, when the drive target transmitted to it via the torsion spring 40 is only the pressure roller 23b, its load torque is 2.0 kgf cm, and the spring constant of the torsion spring 40 is 0.01 kgf cm / °, the angle deflection T1 is set to 180°. In this case, before the motor M starts, a torque of 1.8 kgf cm (i.e., the initial torque) is applied to the output gear 52 by the elastic force of the torsion spring 40. This initial torque is less than the load torque of the pressure roller 23b, so that the initial torque will not cause the pressure roller 23b to rotate.

[0180] When the motor M starts, the angle deflection of the torsion spring 40 increases. In this state, the angle deflection of the torsion spring 40, which is in the state of pre-deflection angle T1, further increases, and the torque applied from the torsion spring 40 to the output gear 52 increases. When the torque applied from the torsion spring 40 to the output gear 52 exceeds the load torque of the pressure roller 23b, the pressure roller 23b begins to rotate.

[0181] In this modified example, from the start of motor M until the torque input from motor M to input gear 51 exceeds the initial torque of torsion spring 40, the protrusions 51d and 52d remain in contact, and the input gear 51 and output gear 52 do not rotate relative to each other. When the torque input from motor M to input gear 51 exceeds the initial torque of torsion spring 40, output gear 52 begins to rotate at an angular velocity different from that of input gear 51.

[0182] During the period from the start of motor M until the output gear 52 and pressure roller 23b begin to rotate, the angle deflection of torsion spring 40 increases until an elastic force corresponding to the difference between the load torque of pressure roller 23b and the initial torque of torsion spring 40 is generated. In this case, even at the point when motor M starts, torsion spring 40 deflects by an angle T1 corresponding to the initial torque. Therefore, compared to the first embodiment where torsion spring 40 does not deflect at the point when motor M starts, the waiting time for pressure roller 23b to begin rotating can be shortened.

[0183] Relationship between pressure roller and sheet discharge roller

[0184] like Figure 3AAs shown, according to the first embodiment, the sheet discharge roller 24a, which is disposed downstream of the pressure roller 23b in the sheet conveying direction, also receives the driving force of the motor M via the drive transmission unit DT including the torsion spring 40. Therefore, during the time period between when the leading edge of the sheet S has reached the clamping portion of the sheet discharge roller pair 24 and before the trailing edge of the sheet S has passed the transfer clamping portion Nt, by pulling the sheet S with the sheet discharge roller pair 24, the slippage of the sheet S relative to the intermediate transfer belt 13 can be suppressed.

[0185] When the sheet S is held and conveyed by both the fixing clamping part Nf and the clamping part of the sheet discharge roller pair 24, a circumferential speed difference may occur between the pressure roller 23b and the sheet discharge roller 24a due to factors such as thermal expansion or wear of the rollers. If the sheet S becomes tense or slack between the fixing clamping part Nf and the clamping part of the sheet discharge roller pair 24 due to the circumferential speed difference, the angular velocity of the pressure roller 23b may change due to the force applied from the sheet S. If the angular velocity of the pressure roller 23b changes during the transfer of the toner image, even if the sheet S does not slip, the change in the position of the sheet S may affect the transfer accuracy of the toner image at the transfer clamping part Nt.

[0186] Therefore, according to this embodiment, both the pressure roller 23b and the sheet discharge roller 24a are configured to receive the driving force of the motor M via the torsion spring 40. Thus, when tension is applied to the sheet S between the fixing clamping portion Nf and the clamping portion of the sheet discharge roller pair 24, the load torque of the pressure roller 23b decreases due to the force received from the sheet S, while the load torque of the sheet discharge roller 24a increases due to the force applied from the sheet S. Conversely, when the sheet S relaxes between the fixing clamping portion Nf and the clamping portion of the sheet discharge roller pair 24, the load torque of the pressure roller 23b increases due to the force applied from the sheet S, while the load torque of the sheet discharge roller 24a decreases due to the force applied from the sheet S.

[0187] That is, according to the configuration of the first embodiment in which the drive transmission path to the pressure roller 23b and the sheet discharge roller 24a branches downstream of the torsion spring 40, the effect of the circumferential speed difference between the pressure roller 23b and the sheet discharge roller 24a is canceled out. Therefore, rapid changes in the angular velocity of the pressure roller 23b can be suppressed, and the effect of the circumferential speed difference between the pressure roller 23b and the sheet discharge roller 24a on the transfer accuracy of the toner image can be suppressed.

[0188] Used in combination with the ring control between the transfer clamp and the fixing clamp.

[0189] like Figure 3BAs shown in the modified example, if a motor M1 that drives the drive roller 14, independent of the motor M that drives the pressure roller 23b, is provided, a sensor 60 can be provided to control the slack of the sheet S between the transfer clamping section Nt and the fixing clamping section Nf. The sensor 60 is arranged between the transfer clamping section Nt and the fixing clamping section Nf to detect the sheet S at a predetermined detection position along the thickness direction of the sheet S in the sheet transport path.

[0190] The control unit of the image forming apparatus 100 can determine, based on the detection results of the sensor 60, whether the slack (i.e., circulation) of the sheet S between the transfer clamping section Nt and the fixing clamping section Nf is appropriate. If the slack of the sheet S is too small, the control unit increases the rotational speed of the motor M to prevent the sheet S from being pulled between the transfer clamping section Nt and the fixing clamping section Nf. If the slack of the sheet S is too large, the control unit decreases the rotational speed of the motor M to prevent the sheet S from scratching the guide forming the sheet transport path and to prevent scratches from forming on the image.

[0191] However, using only sensor 60 for slack control (i.e., loop control) may result in difficulty in accurately controlling the slack amount, for example, due to detection errors of sensor 60. Furthermore, especially when using thick paper with high rigidity as the sheet S, the suitable range of slack amount is small, and it may be difficult to bring the slack amount into the appropriate range simply by controlling the speed of motor M.

[0192] At the same time, according to Figure 3B The modified example combines speed control of motor M with a torsion spring 40 capable of absorbing the circumferential speed difference between the intermediate transfer belt 13 and the pressure roller 23b. This results in more stable conveying of the sheet S.

[0193] Other modification examples

[0194] According to the first embodiment, a construction using a torsion spring 40 as an elastic member is described, but a compression spring, a tension spring, or other elastic member (e.g., rubber) may also be used as the elastic member.

[0195] Second Embodiment

[0196] The description is used as a second embodiment, another example. In the following description, unless otherwise noted, elements having substantially the same configuration and effect as those described in the first embodiment are indicated by the same reference numerals as in the first embodiment, and the parts that differ from the first embodiment will be described below mainly.

[0197] According to this embodiment, the alignment roller 20b is an example of a first conveying member that contacts and rotates with the sheet S to convey the sheet S in the sheet conveying direction. Furthermore, the alignment roller 20b is arranged adjacent to the transfer clamping portion Nt in the sheet conveying direction.

[0198] According to the image forming apparatus 100 of the first embodiment, the alignment roller pair 20a, which is arranged adjacent to and upstream of the transfer clamping portion Nt in the sheet conveying direction, generally has a holding force (i.e., pressing force) set to a relatively high value. This is because if the sheet S slides relative to the alignment roller pair 20a, the sheet S may become skewed, or the position of the sheet S at the transfer clamping portion Nt may be disturbed, which may lead to image defects.

[0199] However, due to the high holding force (i.e., pressing force) of the alignment roller on 20a, image defects may occur if there is a circumferential speed deviation between the alignment roller 20b and the intermediate transfer belt 13. That is, due to the circumferential speed difference, the sheet S may be pulled or relaxed between the alignment clamping part Nr and the transfer clamping part Nt, causing the sheet S to slide relative to the intermediate transfer belt 13 and potentially resulting in image defects.

[0200] Meanwhile, the transport rollers of the image forming apparatus 100, including the alignment roller 20b, will wear down due to repeated image forming operations, and the roller diameter (i.e., the outer diameter) will gradually decrease. Even with a fixed angular velocity of the alignment roller 20b, its circumferential speed will slow down as the roller diameter decreases. Furthermore, the roller diameter of the transport rollers of the image forming apparatus 100, including the alignment roller 20b, may also vary due to manufacturing tolerances and environmental conditions (such as temperature and humidity). For these reasons, when there is a deviation in the circumferential speed between the alignment roller 20b and the intermediate transfer belt 13, the aforementioned image defects may occur.

[0201] Therefore, according to this embodiment, as Figure 12 As shown, the drive is transmitted to the alignment roller 20b via the drive transmission unit DT', which includes a torsion spring 42. The elastic deformation of the torsion spring 42 allows the circumferential speed of the alignment roller 20b to vary according to the circumferential speed of the intermediate transfer belt 13, thereby suppressing image defects.

[0202] like Figure 12 As shown, the drive transmission unit DT' includes an input gear 61 serving as a first rotating member (i.e., an input-side rotating member), an output gear 62 serving as a second rotating member (i.e., an output-side rotating member), and a torsion spring 42 serving as an elastic member. The actual configuration of the drive transmission unit DT' can be similar to the drive transmission unit DT described according to the first embodiment or a modified example thereof.

[0203] The pressing force of the alignment roller pair 20a is typically high, resulting in a higher load torque required to rotate the alignment roller 20b. The load torque of the alignment roller 20b includes the rotational resistance of the alignment roller 20b caused by friction against the bearings supporting it, and the frictional resistance received by the alignment roller 20b from the alignment driven roller 20c due to the rotational resistance of the alignment driven roller 20c facing it. Furthermore, the load torque of the alignment roller 20b may also include the force received by the alignment roller 20b from the sheet S being pulled by a conveying member (in this embodiment, a separating roller pair 21) positioned upstream of the alignment roller pair 20a, i.e., the reverse tension. Taking these factors into account, the load torque of the alignment roller 20b required for stable conveying of the sheet S can be set. The load torque of the alignment roller 20b can be obtained experimentally.

[0204] Unlike the pressure roller 23b, the alignment roller 20b is located far from the heater 23c, which serves as a heat source, resulting in relatively small effects of thermal expansion on the alignment roller 20b. However, considering the wear of the alignment roller 20b or the manufacturing tolerances of the alignment roller 20b and the belt drive roller 14, a circumferential speed difference may occur between the alignment roller 20b and the intermediate transfer belt 13. In the following description, it is assumed that a speed difference of approximately 1% may occur between the alignment roller 20b and the intermediate transfer belt 13. Based on this speed difference, for example, while the intermediate transfer belt 13 rotates a circumferential movement distance corresponding to the long side of the A4 size sheet S (i.e., 297 mm), the alignment roller 20b rotates a circumferential movement distance approximately 3 mm longer than the intermediate transfer belt 13 (i.e., 300 mm).

[0205] According to this embodiment, the circumferential speed of the alignment roller 20b is set to account for the gradual decrease in the circumferential speed of the alignment roller 20b due to wear as the cumulative number of image forming operations increases. That is, when the image forming apparatus 100 is shipped, the circumferential speed of the alignment roller 20b is set to a value that is 0.7% faster than the circumferential speed of the intermediate transfer belt 13.

[0206] like Figure 11A As shown, if the circumferential speed VR of the alignment roller 20b corresponds to the circumferential speed VB of the intermediate transfer belt 13, image defects caused by the difference in circumferential speed will not occur. Figures 11A to 11C In the image formation process, with the circumferential speed VB of the intermediate transfer belt 13 at 100%, the circumferential speed of the alignment roller 20b is displayed as a percentage.

[0207] like Figure 11BAs shown, when the circumferential speed VR of the alignment roller 20b is set to be 0.7% faster than the circumferential speed VB of the intermediate transfer belt 13, the alignment roller 20b conveys the sheet S to press the sheet S toward the transfer clamping part Nt. In this state, the holding force Fr of the sheet S at the alignment clamping part Nr is greater than the holding force Ft of the sheet S at the transfer clamping part Nt. Therefore, if Figure 11B If this state continues, the sheet S may slide relative to the intermediate transfer belt 13 at the transfer clamping part Nt.

[0208] like Figure 11C As shown, according to this embodiment, the circumferential speed difference between the alignment roller 20b and the intermediate transfer belt 13 is absorbed by the elastic deformation of the torsion spring 42, allowing the drive to be transmitted to the alignment roller 20b at a circumferential speed VR equal to the circumferential speed VB of the intermediate transfer belt 13. That is, the elastic deformation of the torsion spring 42 allows for a rotational delay of the alignment roller 20b compared to the circumferential speed at which the leading edge of the sheet S reaches the transfer clamping portion Nt. Therefore, the pushing force of the alignment roller on the sheet S by the alignment roller 20a is reduced.

[0209] like Figure 11C As shown, while the sheet S is held by both the clamping portion of the alignment roller 20b and the transfer clamping portion Nt, the angle deflection of the torsion spring 42 gradually increases. With the increase in the angle deflection of the torsion spring 42, the torque transmitted from the torsion spring 42 to the output gear 62 increases, and the force (i.e., the pushing force) exerted by the alignment roller 20b on the sheet S in the sheet conveying direction increases. However, if the pushing force corresponding to the maximum angle deflection during the time period during which the sheet S is held by both the clamping portion of the alignment roller 20b and the transfer clamping portion Nt is less than the holding force Ft of the sheet S at the transfer clamping portion Nt, then slippage of the sheet S will not occur at the transfer clamping portion Nt. That is, by considering the maximum angle deflection during the aforementioned time period, the spring constant of the torsion spring 42 is set to prevent slippage of the sheet S at the transfer clamping portion Nt.

[0210] It has been described that the circumferential speed VR of the alignment roller 20b is set to be faster than the circumferential speed VB of the intermediate transfer belt 13. However, as the wear of the alignment roller 20b intensifies, its circumferential speed VR becomes slower than the circumferential speed VB of the intermediate transfer belt 13. Even in this case, the difference in circumferential speed between the alignment roller 20b and the intermediate transfer belt 13 is absorbed by the elastic deformation of the torsion spring 42. That is, through the elastic deformation of the torsion spring 42, the rotation of the alignment roller 20b is allowed to accelerate compared to the circumferential speed in the state before the leading edge of the sheet S reaches the transfer clamping part Nt. Therefore, the occurrence of image defects caused by the alignment rollers pulling the sheet S can be suppressed.

[0211] Reference Figures 13A to 13C The description covers the variation of the angular velocity of the element involved in the drive transmission from motor M to alignment roller 20b according to this embodiment.

[0212] Figure 13A This shows the state after the leading edge of the sheet S has passed the alignment clamping part Nr and before the leading edge of the sheet S reaches the transfer clamping part Nt. Figure 13B The diagram shows the state after the leading edge of the sheet S has reached the transfer clamping part Nt and before the trailing edge of the sheet S passes the alignment clamping part Nr. Figure 13C The diagram shows the state after the trailing edge of sheet S has passed through the alignment clamping part Nr and before the trailing edge of sheet S has passed through the transfer clamping part Nt.

[0213] exist Figures 13A to 13C In this diagram, the angular velocity of the output shaft of motor M is referred to as RM, and the angular velocity of the alignment roller 20b is referred to as RR. The angular velocity on the input side of torsion spring 42 is referred to as RT1, and the angular velocity on the output side of torsion spring 42 is referred to as RT2. The angular velocity RT1 on the input side of torsion spring 42 is determined based on the angular velocity RM of the output shaft of motor M and the reduction ratio of the drive transmission mechanism DT1 from the output shaft of motor M to the input gear 51. The angular velocity RR of alignment roller 20b is determined based on the angular velocity RT2 on the output side of torsion spring 42 and the reduction ratio of the drive transmission mechanism DT2 from the output gear 52 to the alignment roller 20b.

[0214] like Figure 13A As shown, before the leading edge of the sheet S reaches the transfer clamping part Nt, the angular velocity RT2 on the output side of the torsion spring 42 is equal to the angular velocity RT1 on the input side.

[0215] like Figure 13B As shown, when the sheet S is held by both the alignment clamping part Nr and the transfer clamping part Nt, and... Figure 13A Compared to the previous state, the angular velocity RR of the alignment roller 20b is delayed by 0.7%. Furthermore, due to the elastic deformation of the torsion spring 42, the angular velocity RT2 on the output side of the torsion spring 42 is allowed to be delayed by 0.7% relative to the angular velocity RT1 on the input side of the torsion spring 42. That is, the circumferential speed difference between the alignment roller 20b and the intermediate transfer belt 13 is absorbed by the elastic deformation of the torsion spring 42.

[0216] like Figure 13C As shown, after the trailing edge of sheet S has passed the alignment clamping part Nr, the angular velocity RR of the alignment roller 20b becomes greater than... Figure 13AThe state is fast. Furthermore, the angular velocity RT2 on the output side of the torsion spring 42 becomes faster than the angular velocity RT1 on the input side of the torsion spring 42. This is because when the trailing edge of the sheet S has passed through the transfer clamping part Nr and the tension is released, a portion of the elastic deformation of the torsion spring 42 recovers, causing the output side of the torsion spring 42 to temporarily rotate faster than the input side. Furthermore, if the angular deflection of the torsion spring 42 becomes equal to... Figure 13A Under normal conditions, the angular velocity RR of the alignment roller 20b and the angular velocity RT2 on the output side of the torsion spring 42 will be equal to... Figure 13A The state.

[0217] Even according to the construction of this embodiment, due to the elastic deformation of the torsion spring 42 (i.e., the elastic member), it is possible to transmit driving force to the alignment roller 20b (i.e., the first conveying member) when the angular velocity of the input gear 61 (i.e., the first rotating member) is different from the angular velocity of the output gear 62 (i.e., the second rotating member). In other words, the torsion spring 42 (i.e., the elastic member) can deform to allow the alignment roller 20b (i.e., the first conveying member) to rotate when the angular velocities of the input gear 61 (i.e., the first rotating member) driven by the motor M and the output gear 62 (i.e., the second rotating member) are different from each other. Thus, the alignment roller 20b is allowed to rotate at a circumferential speed corresponding to the circumferential speed of the intermediate transfer belt 13. As a result, the disadvantages caused by the slack or pulling of the sheet S between the alignment roller 20b and the intermediate transfer belt 13 can be suppressed.

[0218] That is, according to this embodiment, a sheet conveying device and an image forming device that can convey sheet material more stably can be provided.

[0219] Modify Example

[0220] like Figures 14A to 14C As shown, a torque limiter 42T can be used instead of the torsion spring 42. In this case, the advantage is that the driving force becomes substantially constant and independent of the difference in feed rate. Meanwhile, the configuration using the torsion spring 42 can be achieved at a lower cost.

[0221] Third Embodiment

[0222] Reference Figure 15 A third embodiment is described as another embodiment. In the following description, unless otherwise noted, elements having substantially the same configuration and effect as those described in the first embodiment are indicated by the same reference numerals as in the first embodiment, and therefore the parts that differ from the first embodiment will be described below mainly.

[0223] The image forming apparatus 101 according to this embodiment is a so-called electrostatic conveyor type electrophotographic color image forming apparatus, wherein four processing cartridges PY, PM, PC, and PK are arranged along a conveyor belt 113. The conveyor belt 113 is stretched across multiple rollers 114 and 116 and is driven to rotate counterclockwise in the figure during image forming. The sheet S fed from the alignment roller pair 20a is electrostatically carried on the conveyor belt 113 and is conveyed toward the fixing unit 23 via four transfer clamping parts Nt. The transfer clamping part Nt is the portion from which the toner image is transferred from each of the photosensitive drums 1 of each of the processing cartridges PY, PM, PC, and PK to the sheet S, and it is a clamping portion formed between each photosensitive drum 1 and the conveyor belt 113.

[0224] The pressure roller 23b of the fixing unit 23 is driven by a motor M3, which serves as the drive source. The driving force of the motor M3 is transmitted to the pressure roller 23b via a drive transmission unit DT, which includes a torsion spring 40. The configuration of the drive transmission unit DT associated with the driving of the pressure roller 23b can be the same as that described in the first embodiment or its modified examples. According to this configuration, similar advantages as those of the first embodiment or its modified examples can be obtained.

[0225] Alignment roller 20b of alignment roller pair 20a is driven by motor M4, which serves as the drive source. The driving force of motor M4 is transmitted to alignment roller 20b via drive transmission unit DT', which includes torsion spring 42. The configuration of drive transmission unit DT' associated with the driving of alignment roller 20b can be the same as that described in the second embodiment.

[0226] The drive source for driving the rollers 114 or 116 that rotate the conveyor belt 113 can be the same as motor M3 or motor M4. Furthermore, motor M3 and motor M4 can be the same motor. With this configuration, similar advantages to the second embodiment can be obtained.

[0227] Each of the pressure roller 23b and alignment roller 20b described above is an example of a first conveying member. With the pressure roller 23b referred to as the first conveying member, a conveying member driven by the same drive source as the pressure roller 23b (i.e., motor M3) and arranged to simultaneously contact the sheet S with the pressure roller 23b can be referred to as a second conveying member. With the motor M3 driving rollers 114 or 116, the conveyor belt 113 serves as an example of a second conveying member.

[0228] With the alignment roller 20b referred to as the first conveying member, a conveying member driven by the same drive source as the alignment roller 20b (i.e., motor M4) and arranged to contact the sheet S simultaneously with the alignment roller 20b can be referred to as the second conveying member. With the motor M4 driving rollers 114 or 116, the conveyor belt 113 serves as an example of the second conveying member.

[0229] Other modifications

[0230] The "image forming apparatus" according to this disclosure is not limited to an electrophotographic system, and may be, for example, an inkjet printer.

[0231] According to various embodiments, the elastic member that absorbs the velocity difference between the first rotating member and the second rotating member is a torsion spring. However, springs other than torsion springs can be used as elastic members. For example, compression springs that compress in the rotational direction can be used. However, torsion springs are preferred as elastic members because they have a wide elastic range in the rotational direction.

[0232] According to this disclosure, sheet conveying equipment and image forming equipment that can convey sheets more stably can be provided.

[0233] Other embodiments

[0234] While this disclosure has been described with reference to embodiments, it should be understood that this disclosure is not limited to the disclosed embodiments. The scope of the following claims should be interpreted in the broadest possible sense to include all such modifications and equivalent structures and functions.

Claims

1. A sheet conveying device, comprising: A first conveying member is configured to rotate while in contact with the sheet to convey the sheet in a sheet conveying direction. A second conveying member is disposed at a position different from that of the first conveying member in the sheet conveying direction. During at least a portion of the time period during which the first conveying member is in contact with the sheet, the second conveying member is configured to rotate while in contact with the sheet to convey the sheet. A motor configured to drive the first conveying member and the second conveying member; A first rotating member is connected to the motor and configured to rotate; A second rotating member is connected to the first conveying member and is configured to rotate; as well as An elastic member engages with the first rotating member and the second rotating member, the elastic member being deformable to allow the first conveying member to rotate when the angular velocity of the first rotating member driven by the motor is different from the angular velocity of the second rotating member.

2. The sheet conveying device according to claim 1, The first conveying member includes a first contact surface configured to contact the sheet. The second conveying member includes a second contact surface configured to contact the sheet. In the first state, the circumferential velocity of the first contact surface is referred to as the first velocity, and in the first state, the circumferential velocity of the second contact surface is referred to as the second velocity. The elastic member can deform to allow the circumferential velocity of the first contact surface in the second state to be a third velocity. The first state is a state in which the first and second conveying members are driven by the motor and the sheet is separated from at least one of the first and second contact surfaces. In the second state, the first and second conveying members are driven by the motor and the sheet is in contact with both the first and second contact surfaces. The speed difference between the third speed and the second speed is less than the speed difference between the first speed and the second speed.

3. The sheet conveying device according to claim 2, The first speed is faster than the second speed, and The third speed is slower than the first speed.

4. The sheet conveying device according to any one of claims 1 to 3, further comprising: A first transmission component pair, the first transmission component pair including a first transmission component and a first opposing component opposite to the first transmission component; as well as The second transmission member pair includes the second transmission member and a second opposing member opposite to the second transmission member. In the case where the state in which the sheet is held by the first pair of conveying members and the second pair of conveying members is called the holding state, the position of the sheet when the holding state ends is called the release position, and the state in which the angular velocity of the first rotating member is different from the angular velocity of the second rotating member is called the different velocity state, the elastic member can deform such that when the sheet reaches the release position, the first rotating member and the second rotating member are in the different velocity state.

5. The sheet conveying device according to any one of claims 1 to 3, further comprising: A first transmission component pair, the first transmission component pair including a first transmission component and a first opposing component opposite to the first transmission component; as well as The second transmission member pair includes the second transmission member and a second opposing member opposite to the second transmission member. Wherein the state in which the sheet is held by both the first pair of conveying members and the second pair of conveying members is referred to as the holding state, and the position of the sheet when the holding state ends is referred to as the release position, the elastic member is configured to allow the angular velocity of the second rotating member to be slower than the angular velocity of the first rotating member when the sheet reaches the release position.

6. The sheet conveying device according to any one of claims 1 to 3, further comprising: A first transmission component pair, the first transmission component pair including a first transmission component and a first opposing component opposite to the first transmission component; as well as The second transmission member pair includes the second transmission member and a second opposing member opposite to the second transmission member. Wherein the state in which the sheet is held by both the first pair of conveying members and the second pair of conveying members is referred to as the holding state, and the position of the sheet when the holding state ends is referred to as the release position, when the sheet reaches the release position, the amount of deformation of the elastic member is within 30% of the amount of deformation of the elastic member corresponding to the maximum allowable stress.

7. The sheet conveying device according to any one of claims 1 to 3, The first rotating member and the second rotating member are configured to rotate about a common axis of rotation.

8. The sheet conveying device according to claim 7, The elastic member is a torsion helical spring, one end of which engages with the first rotating member and the other end with the second rotating member, and the torsion helical spring is configured to deflect about the axis of rotation.

9. The sheet conveying device according to claim 8, The first rotating member includes a first engaging portion that engages with one end of the elastic member. The second rotating member includes a second engaging portion that engages with the other end of the elastic member, and The first joining portion is located away from the second joining portion in the direction of the rotation axis.

10. The sheet conveying device according to claim 8, When the first rotating member is stopped, the first rotating member and the second rotating member are in contact, such that their relative rotation is restricted and the elastic member is in a state of deformation from a free state.

11. The sheet conveying device according to any one of claims 1 to 3, further comprising: A transfer unit configured to form a transfer clamping portion and, while clamping the sheet at the transfer clamping portion, transfer a toner image onto the sheet. The first conveying member is disposed near the transfer clamping part in the sheet conveying direction.

12. The sheet conveying device according to claim 11, The second conveying member is disposed in the transfer unit and configured to contact the sheet at the transfer clamping portion.

13. The sheet conveying device according to any one of claims 1 to 3, further comprising: A fixing unit configured to form a fixing clamping portion and fix a toner image onto the sheet while clamping the sheet at the fixing clamping portion. The first conveying component is disposed in the fixing unit.

14. The sheet conveying device according to any one of claims 1 to 3, further comprising: A limiter is connected to the first conveying member and configured to suppress the acceleration of the first conveying member caused by the restoring force of the elastic member when the sheet in contact with the first conveying member separates from the first conveying member.

15. An image forming apparatus comprising: The sheet conveying device according to any one of claims 1 to 14; as well as An image forming section is configured to form an image to be recorded on a sheet conveyed by the sheet conveying device.

Images